<?xml version="1.0" encoding="UTF-8"?>
<rss version="2.0"
	xmlns:content="http://purl.org/rss/1.0/modules/content/"
	xmlns:wfw="http://wellformedweb.org/CommentAPI/"
	xmlns:dc="http://purl.org/dc/elements/1.1/"
	xmlns:atom="http://www.w3.org/2005/Atom"
	xmlns:sy="http://purl.org/rss/1.0/modules/syndication/"
	xmlns:slash="http://purl.org/rss/1.0/modules/slash/"
	xmlns:georss="http://www.georss.org/georss" xmlns:geo="http://www.w3.org/2003/01/geo/wgs84_pos#" xmlns:media="http://search.yahoo.com/mrss/"
	>

<channel>
	<title>Less Incompetence</title>
	<atom:link href="http://maxbaroi.wordpress.com/feed/" rel="self" type="application/rss+xml" />
	<link>http://maxbaroi.wordpress.com</link>
	<description>A blog on whatever from a nobody</description>
	<lastBuildDate>Tue, 28 Jul 2009 08:56:46 +0000</lastBuildDate>
	<language>en</language>
	<sy:updatePeriod>hourly</sy:updatePeriod>
	<sy:updateFrequency>1</sy:updateFrequency>
	<generator>http://wordpress.com/</generator>
<cloud domain='maxbaroi.wordpress.com' port='80' path='/?rsscloud=notify' registerProcedure='' protocol='http-post' />
<image>
		<url>http://s2.wp.com/i/buttonw-com.png</url>
		<title>Less Incompetence</title>
		<link>http://maxbaroi.wordpress.com</link>
	</image>
	<atom:link rel="search" type="application/opensearchdescription+xml" href="http://maxbaroi.wordpress.com/osd.xml" title="Less Incompetence" />
	<atom:link rel='hub' href='http://maxbaroi.wordpress.com/?pushpress=hub'/>
		<item>
		<title>Solutions to Selected Exercises from 245C, Notes 3: Distributions</title>
		<link>http://maxbaroi.wordpress.com/2009/05/19/solutions-to-selected-exercises-from-245c-notes-3-distributions/</link>
		<comments>http://maxbaroi.wordpress.com/2009/05/19/solutions-to-selected-exercises-from-245c-notes-3-distributions/#comments</comments>
		<pubDate>Wed, 20 May 2009 06:58:43 +0000</pubDate>
		<dc:creator>maxbaroi</dc:creator>
				<category><![CDATA[245C]]></category>

		<guid isPermaLink="false">http://maxbaroi.wordpress.com/?p=103</guid>
		<description><![CDATA[I haven&#8217;t posted anything in a while. Partly because I&#8217;ve been busy with family matters, but mainly because I&#8217;ve actually made some friends this quarter and so instead of typing up solutions by myself, I just talk about the exercises with them. The work is more engaging that way, but that method has the draw [...]<img alt="" border="0" src="http://stats.wordpress.com/b.gif?host=maxbaroi.wordpress.com&amp;blog=6922221&amp;post=103&amp;subd=maxbaroi&amp;ref=&amp;feed=1" width="1" height="1" />]]></description>
			<content:encoded><![CDATA[<p>
I haven&#8217;t posted anything in a while. Partly because I&#8217;ve been busy with family matters, but mainly because I&#8217;ve actually made some friends this quarter and so instead of typing up solutions by myself, I just talk about the exercises with them. The work is more engaging that way, but that method has the draw back of de-motivating me. I feel less of a need to write solutions up when I already went over them with an actual audience. But things have calmed down a bit, and now I&#8217;m less busy than I was, so I now plan to update more regularly.</p>
<p>
Quick aside. Does anyone know how to allow WordPress to understand user-defined Latex commands? [Edit: Professor Tao informed me how]</p>
<p>
My hang up is everything looks better fixed-width, but WordPress cuts off some of the equations when I have a fixed-width theme. I don&#8217;t know if that problem was particular to the theme I chose, or whatever, but because of it, I&#8217;ve been forced into this less nice flexible-width theme.</p>
<p>
[Edit: I have finally fixed the known errors in this post. I actually made the corrections at least a month ago, but out of sheer laziness, did not repost until just now.]</p>
<p>
<span id="more-103"></span></p>
<p>
<p><b> Exercise 7 </b></p>
<p><p>
We already know that <img src='http://s0.wp.com/latex.php?latex=%7BC_c%5E%5Cinfty%28%7B%5Cmathbb+R%7D%5Ed%29%5E%2A%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C_c^&#92;infty({&#92;mathbb R}^d)^*}' title='{C_c^&#92;infty({&#92;mathbb R}^d)^*}' class='latex' /> is a vector space (with the conjugate complex structure). So we need to show that it&#8217;s Hausdorff and that vector addition and scalar multiplication are continuous. The proof for each of these statements hinge on <img src='http://s0.wp.com/latex.php?latex=%7B%7B%5Cmathbb+C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{{&#92;mathbb C}}' title='{{&#92;mathbb C}}' class='latex' /> being Hausdorff and that we endowed <img src='http://s0.wp.com/latex.php?latex=%7BC_c%5E%5Cinfty%28%7B%5Cmathbb+R%7D%5Ed%29%5E%2A%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C_c^&#92;infty({&#92;mathbb R}^d)^*}' title='{C_c^&#92;infty({&#92;mathbb R}^d)^*}' class='latex' /> with the weak-<img src='http://s0.wp.com/latex.php?latex=%7B%2A%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{*}' title='{*}' class='latex' /> topology.</p>
<p>
Let <img src='http://s0.wp.com/latex.php?latex=%7B%5Clambda_%5Calpha%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;lambda_&#92;alpha}' title='{&#92;lambda_&#92;alpha}' class='latex' /> be a convergent net in <img src='http://s0.wp.com/latex.php?latex=%7BC_c%5E%5Cinfty%28%7B%5Cmathbb+R%7D%5Ed%29%5E%2A%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C_c^&#92;infty({&#92;mathbb R}^d)^*}' title='{C_c^&#92;infty({&#92;mathbb R}^d)^*}' class='latex' />. Suppose that our sequence converges to two distributions, <img src='http://s0.wp.com/latex.php?latex=%7B%5Clambda%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;lambda}' title='{&#92;lambda}' class='latex' /> and <img src='http://s0.wp.com/latex.php?latex=%7B%5Clambda%5E%5Cprime%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;lambda^&#92;prime}' title='{&#92;lambda^&#92;prime}' class='latex' />. Then for each test function <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' />, <img src='http://s0.wp.com/latex.php?latex=%7B%5Clangle+f%2C+%5Clambda_%5Calpha+%5Crangle+%5Crightarrow+%5Clangle+f%2C+%5Clambda+%5Crangle+%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;langle f, &#92;lambda_&#92;alpha &#92;rangle &#92;rightarrow &#92;langle f, &#92;lambda &#92;rangle }' title='{&#92;langle f, &#92;lambda_&#92;alpha &#92;rangle &#92;rightarrow &#92;langle f, &#92;lambda &#92;rangle }' class='latex' />, and <img src='http://s0.wp.com/latex.php?latex=%7B%5Clangle+f%2C+%5Clambda_%5Calpha+%5Crangle+%5Crightarrow+%5Clangle+f%2C+%5Clambda%5E%5Cprime+%5Crangle+%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;langle f, &#92;lambda_&#92;alpha &#92;rangle &#92;rightarrow &#92;langle f, &#92;lambda^&#92;prime &#92;rangle }' title='{&#92;langle f, &#92;lambda_&#92;alpha &#92;rangle &#92;rightarrow &#92;langle f, &#92;lambda^&#92;prime &#92;rangle }' class='latex' /> in <img src='http://s0.wp.com/latex.php?latex=%7B%7B%5Cmathbb+C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{{&#92;mathbb C}}' title='{{&#92;mathbb C}}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7B%7B%5Cmathbb+C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{{&#92;mathbb C}}' title='{{&#92;mathbb C}}' class='latex' /> with its usual topology is Hausdorff, so convergent sequences have only one limit. Since <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7B%5Clangle+f%2C+%5Clambda_%5Calpha+%5Crangle%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{&#92;langle f, &#92;lambda_&#92;alpha &#92;rangle&#92;}}' title='{&#92;{&#92;langle f, &#92;lambda_&#92;alpha &#92;rangle&#92;}}' class='latex' /> converges to both <img src='http://s0.wp.com/latex.php?latex=%7B%5Clangle+f%2C+%5Clambda+%5Crangle%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;langle f, &#92;lambda &#92;rangle}' title='{&#92;langle f, &#92;lambda &#92;rangle}' class='latex' /> and <img src='http://s0.wp.com/latex.php?latex=%7B%5Clangle+f%2C+%5Clambda%5E%5Cprime+%5Crangle%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;langle f, &#92;lambda^&#92;prime &#92;rangle}' title='{&#92;langle f, &#92;lambda^&#92;prime &#92;rangle}' class='latex' />, that must mean that they are equal. Therefore, <img src='http://s0.wp.com/latex.php?latex=%7B%5Clangle+f%2C+%5Clambda+%5Crangle+%3D+%5Clangle+f%2C+%5Clambda%5E%5Cprime+%5Crangle%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;langle f, &#92;lambda &#92;rangle = &#92;langle f, &#92;lambda^&#92;prime &#92;rangle}' title='{&#92;langle f, &#92;lambda &#92;rangle = &#92;langle f, &#92;lambda^&#92;prime &#92;rangle}' class='latex' /> for all test functions <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' />. Thus <img src='http://s0.wp.com/latex.php?latex=%7B%5Clambda+%3D+%5Clambda%5E%5Cprime%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;lambda = &#92;lambda^&#92;prime}' title='{&#92;lambda = &#92;lambda^&#92;prime}' class='latex' />. Every convergent sequence in <img src='http://s0.wp.com/latex.php?latex=%7BC_c%5E%5Cinfty%28%7B%5Cmathbb+R%7D%5Ed%29%5E%2A%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C_c^&#92;infty({&#92;mathbb R}^d)^*}' title='{C_c^&#92;infty({&#92;mathbb R}^d)^*}' class='latex' /> has only one limit point. Therefore <img src='http://s0.wp.com/latex.php?latex=%7BC_c%5E%5Cinfty%28%7B%5Cmathbb+R%7D%5Ed%29%5E%2A%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C_c^&#92;infty({&#92;mathbb R}^d)^*}' title='{C_c^&#92;infty({&#92;mathbb R}^d)^*}' class='latex' /> is Hausdorff when endowed with weak-<img src='http://s0.wp.com/latex.php?latex=%7B%2A%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{*}' title='{*}' class='latex' /> topology.</p>
<p>
Now suppose that the net <img src='http://s0.wp.com/latex.php?latex=%7B%28%5Clambda_%5Calpha%2C+%5Ckappa_%5Calpha%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{(&#92;lambda_&#92;alpha, &#92;kappa_&#92;alpha)}' title='{(&#92;lambda_&#92;alpha, &#92;kappa_&#92;alpha)}' class='latex' /> converges to <img src='http://s0.wp.com/latex.php?latex=%7B%28%5Clambda%2C+%5Ckappa%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{(&#92;lambda, &#92;kappa)}' title='{(&#92;lambda, &#92;kappa)}' class='latex' /> in <img src='http://s0.wp.com/latex.php?latex=%7BC_c%5E%5Cinfty%28%7B%5Cmathbb+R%7D%5Ed%29%5E%2A+%5Ctimes+C_c%5E%5Cinfty%28%7B%5Cmathbb+R%7D%5Ed%29%5E%2A%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C_c^&#92;infty({&#92;mathbb R}^d)^* &#92;times C_c^&#92;infty({&#92;mathbb R}^d)^*}' title='{C_c^&#92;infty({&#92;mathbb R}^d)^* &#92;times C_c^&#92;infty({&#92;mathbb R}^d)^*}' class='latex' /> with the product topology. So we&#8217;re given that <img src='http://s0.wp.com/latex.php?latex=%7B%5Clambda_%5Calpha+%5Crightarrow+%5Clambda%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;lambda_&#92;alpha &#92;rightarrow &#92;lambda}' title='{&#92;lambda_&#92;alpha &#92;rightarrow &#92;lambda}' class='latex' />, and <img src='http://s0.wp.com/latex.php?latex=%7B%5Ckappa_%5Calpha+%5Crightarrow+%5Ckappa%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;kappa_&#92;alpha &#92;rightarrow &#92;kappa}' title='{&#92;kappa_&#92;alpha &#92;rightarrow &#92;kappa}' class='latex' />, we need to show that <img src='http://s0.wp.com/latex.php?latex=%7B%5Clambda_%5Calpha%2B%5Ckappa_%5Calpha+%5Crightarrow+%5Clambda%2B%5Ckappa%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;lambda_&#92;alpha+&#92;kappa_&#92;alpha &#92;rightarrow &#92;lambda+&#92;kappa}' title='{&#92;lambda_&#92;alpha+&#92;kappa_&#92;alpha &#92;rightarrow &#92;lambda+&#92;kappa}' class='latex' />. For any test function <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' />, we know that <img src='http://s0.wp.com/latex.php?latex=%7B%5Clangle+f%2C+%5Clambda_%5Calpha+%5Crangle+%5Crightarrow+%5Clangle+f%2C+%5Clambda+%5Crangle+%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;langle f, &#92;lambda_&#92;alpha &#92;rangle &#92;rightarrow &#92;langle f, &#92;lambda &#92;rangle }' title='{&#92;langle f, &#92;lambda_&#92;alpha &#92;rangle &#92;rightarrow &#92;langle f, &#92;lambda &#92;rangle }' class='latex' />, and <img src='http://s0.wp.com/latex.php?latex=%7B%5Clangle+f%2C+%5Ckappa_%5Calpha+%5Crangle+%5Crightarrow+%5Clangle+f%2C+%5Ckappa+%5Crangle+%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;langle f, &#92;kappa_&#92;alpha &#92;rangle &#92;rightarrow &#92;langle f, &#92;kappa &#92;rangle }' title='{&#92;langle f, &#92;kappa_&#92;alpha &#92;rangle &#92;rightarrow &#92;langle f, &#92;kappa &#92;rangle }' class='latex' />. Since for each <img src='http://s0.wp.com/latex.php?latex=%7Bn%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{n}' title='{n}' class='latex' />, <img src='http://s0.wp.com/latex.php?latex=%7B%5Clangle+f%2C+%5Clambda_%5Calpha%2B%5Ckappa_%5Calpha+%5Crangle+%3D+%5Clangle+f%2C+%5Clambda_%5Calpha+%5Crangle+%2B+%5Clangle+f%2C+%5Ckappa_%5Calpha+%5Crangle%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;langle f, &#92;lambda_&#92;alpha+&#92;kappa_&#92;alpha &#92;rangle = &#92;langle f, &#92;lambda_&#92;alpha &#92;rangle + &#92;langle f, &#92;kappa_&#92;alpha &#92;rangle}' title='{&#92;langle f, &#92;lambda_&#92;alpha+&#92;kappa_&#92;alpha &#92;rangle = &#92;langle f, &#92;lambda_&#92;alpha &#92;rangle + &#92;langle f, &#92;kappa_&#92;alpha &#92;rangle}' class='latex' />, we therefore see that <img src='http://s0.wp.com/latex.php?latex=%7B%5Clangle+f%2C+%5Clambda_%5Calpha%2B%5Ckappa_%5Calpha+%5Crangle+%5Crightarrow+%5Clangle+f%2C+%5Clambda+%5Crangle+%2B+%5Clangle+f%2C+%5Ckappa+%5Crangle%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;langle f, &#92;lambda_&#92;alpha+&#92;kappa_&#92;alpha &#92;rangle &#92;rightarrow &#92;langle f, &#92;lambda &#92;rangle + &#92;langle f, &#92;kappa &#92;rangle}' title='{&#92;langle f, &#92;lambda_&#92;alpha+&#92;kappa_&#92;alpha &#92;rangle &#92;rightarrow &#92;langle f, &#92;lambda &#92;rangle + &#92;langle f, &#92;kappa &#92;rangle}' class='latex' />, which is <img src='http://s0.wp.com/latex.php?latex=%7B%5Clangle+f%2C+%5Clambda+%2B+%5Ckappa+%5Crangle%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;langle f, &#92;lambda + &#92;kappa &#92;rangle}' title='{&#92;langle f, &#92;lambda + &#92;kappa &#92;rangle}' class='latex' />. Since this holds for each test function <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' />, we see that <img src='http://s0.wp.com/latex.php?latex=%7B%5Clambda_%5Calpha%2B%5Ckappa_%5Calpha+%5Crightarrow+%5Clambda%2B%5Ckappa%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;lambda_&#92;alpha+&#92;kappa_&#92;alpha &#92;rightarrow &#92;lambda+&#92;kappa}' title='{&#92;lambda_&#92;alpha+&#92;kappa_&#92;alpha &#92;rightarrow &#92;lambda+&#92;kappa}' class='latex' /> in the sense of distributions. Vector addition is therefore continuous. </p>
<p>
Now suppose that the net <img src='http://s0.wp.com/latex.php?latex=%7B%28%5Clambda_%5Calpha%2C+c_%5Calpha%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{(&#92;lambda_&#92;alpha, c_&#92;alpha)}' title='{(&#92;lambda_&#92;alpha, c_&#92;alpha)}' class='latex' /> converges to <img src='http://s0.wp.com/latex.php?latex=%7B%28%5Clambda%2C+c%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{(&#92;lambda, c)}' title='{(&#92;lambda, c)}' class='latex' /> in <img src='http://s0.wp.com/latex.php?latex=%7BC_c%5E%5Cinfty%28%7B%5Cmathbb+R%7D%5Ed%29%5E%2A+%5Ctimes+%7B%5Cmathbb+C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C_c^&#92;infty({&#92;mathbb R}^d)^* &#92;times {&#92;mathbb C}}' title='{C_c^&#92;infty({&#92;mathbb R}^d)^* &#92;times {&#92;mathbb C}}' class='latex' /> with the product topology. So we&#8217;re given that <img src='http://s0.wp.com/latex.php?latex=%7B%5Clambda_%5Calpha+%5Crightarrow+%5Clambda%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;lambda_&#92;alpha &#92;rightarrow &#92;lambda}' title='{&#92;lambda_&#92;alpha &#92;rightarrow &#92;lambda}' class='latex' />, and <img src='http://s0.wp.com/latex.php?latex=%7Bc_%5Calpha+%5Crightarrow+c%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{c_&#92;alpha &#92;rightarrow c}' title='{c_&#92;alpha &#92;rightarrow c}' class='latex' />, we need to show that <img src='http://s0.wp.com/latex.php?latex=%7Bc_%5Calpha+%5Clambda_%5Calpha+%5Crightarrow+c+%5Clambda%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{c_&#92;alpha &#92;lambda_&#92;alpha &#92;rightarrow c &#92;lambda}' title='{c_&#92;alpha &#92;lambda_&#92;alpha &#92;rightarrow c &#92;lambda}' class='latex' />. For any test function <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' />, we know that <img src='http://s0.wp.com/latex.php?latex=%7B%5Clangle+f%2C+%5Clambda_%5Calpha+%5Crangle+%5Crightarrow+%5Clangle+f%2C+%5Clambda+%5Crangle+%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;langle f, &#92;lambda_&#92;alpha &#92;rangle &#92;rightarrow &#92;langle f, &#92;lambda &#92;rangle }' title='{&#92;langle f, &#92;lambda_&#92;alpha &#92;rangle &#92;rightarrow &#92;langle f, &#92;lambda &#92;rangle }' class='latex' />, and <img src='http://s0.wp.com/latex.php?latex=%7B%5Coverline%7Bc%7D_%5Calpha+%5Crightarrow+%5Coverline%7Bc%7D+%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;overline{c}_&#92;alpha &#92;rightarrow &#92;overline{c} }' title='{&#92;overline{c}_&#92;alpha &#92;rightarrow &#92;overline{c} }' class='latex' />. Since for each <img src='http://s0.wp.com/latex.php?latex=%7Bn%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{n}' title='{n}' class='latex' />, <img src='http://s0.wp.com/latex.php?latex=%7B%5Clangle+f%2C+c_%5Calpha+%5Clambda_%5Calpha+%5Crangle+%3D+%5Coverline%7Bc%7D_%5Calpha%5Clangle+f%2C%5Clambda_%5Calpha+%5Crangle%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;langle f, c_&#92;alpha &#92;lambda_&#92;alpha &#92;rangle = &#92;overline{c}_&#92;alpha&#92;langle f,&#92;lambda_&#92;alpha &#92;rangle}' title='{&#92;langle f, c_&#92;alpha &#92;lambda_&#92;alpha &#92;rangle = &#92;overline{c}_&#92;alpha&#92;langle f,&#92;lambda_&#92;alpha &#92;rangle}' class='latex' />, we therefore see that <img src='http://s0.wp.com/latex.php?latex=%7B%5Clangle+f%2C+c_%5Calpha+%5Clambda_%5Calpha+%5Crangle+%5Crightarrow+%5Coverline%7Bc%7D+%5Clangle+f%2C+%5Clambda+%5Crangle%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;langle f, c_&#92;alpha &#92;lambda_&#92;alpha &#92;rangle &#92;rightarrow &#92;overline{c} &#92;langle f, &#92;lambda &#92;rangle}' title='{&#92;langle f, c_&#92;alpha &#92;lambda_&#92;alpha &#92;rangle &#92;rightarrow &#92;overline{c} &#92;langle f, &#92;lambda &#92;rangle}' class='latex' />, which is <img src='http://s0.wp.com/latex.php?latex=%7B%5Clangle+f%2C+c%5Clambda+%5Crangle%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;langle f, c&#92;lambda &#92;rangle}' title='{&#92;langle f, c&#92;lambda &#92;rangle}' class='latex' />. Since this holds for each test function <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' />, we see that <img src='http://s0.wp.com/latex.php?latex=%7Bc_%5Calpha+%5Clambda_%5Calpha+%5Crightarrow+c+%5Clambda%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{c_&#92;alpha &#92;lambda_&#92;alpha &#92;rightarrow c &#92;lambda}' title='{c_&#92;alpha &#92;lambda_&#92;alpha &#92;rightarrow c &#92;lambda}' class='latex' /> in the sense of distributions. Scalar multiplication is therefore continuous.</p>
<p>
<img src='http://s0.wp.com/latex.php?latex=%7BC_c%5E%5Cinfty%28%7B%5Cmathbb+R%7D%5Ed%29%5E%2A%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C_c^&#92;infty({&#92;mathbb R}^d)^*}' title='{C_c^&#92;infty({&#92;mathbb R}^d)^*}' class='latex' /> is a Hausdorff topological vector space.</p>
<p>
<p><b> Exercise 8 </b></p>
<p><p>
Let <img src='http://s0.wp.com/latex.php?latex=%7B%5Cphi%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;phi}' title='{&#92;phi}' class='latex' /> be a locally integrable function, if <img src='http://s0.wp.com/latex.php?latex=%7Bm%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{m}' title='{m}' class='latex' /> is the Lebesgue measure, then <img src='http://s0.wp.com/latex.php?latex=%7B%5Coverline%7B%5Cphi%7D+dm%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;overline{&#92;phi} dm}' title='{&#92;overline{&#92;phi} dm}' class='latex' /> is a regular measure and thus a Radon measure on <img src='http://s0.wp.com/latex.php?latex=%7B%7B%5Cmathbb+R%7D%5Ed%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{{&#92;mathbb R}^d}' title='{{&#92;mathbb R}^d}' class='latex' />. If we can show the identification of a complex Radon measure with distributions is injective, then since the identification of locally integrable functions with its induced regular measure is injective, we have shown that the identification of locally integrable functions with distributions is also injective.</p>
<p>
Let <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmu%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mu}' title='{&#92;mu}' class='latex' /> be a Radon measure. <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmu%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mu}' title='{&#92;mu}' class='latex' /> induces a distribution defined on each test function by <img src='http://s0.wp.com/latex.php?latex=%7Bf+%5Crightarrow+%5Clangle+f%2C+%5Cmu+%5Crangle+%3D+%5Cint+f+d%5Coverline%7B%5Cmu%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f &#92;rightarrow &#92;langle f, &#92;mu &#92;rangle = &#92;int f d&#92;overline{&#92;mu}}' title='{f &#92;rightarrow &#92;langle f, &#92;mu &#92;rangle = &#92;int f d&#92;overline{&#92;mu}}' class='latex' />. Suppose we have two Radon measures <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmu_1%2C%5Cmu_2%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mu_1,&#92;mu_2}' title='{&#92;mu_1,&#92;mu_2}' class='latex' /> such that <img src='http://s0.wp.com/latex.php?latex=%7B%5Cint+f+d%5Coverline%7B%5Cmu%7D_1%3D+%5Cint+f+d%5Coverline%7B%5Cmu%7D_2+%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;int f d&#92;overline{&#92;mu}_1= &#92;int f d&#92;overline{&#92;mu}_2 }' title='{&#92;int f d&#92;overline{&#92;mu}_1= &#92;int f d&#92;overline{&#92;mu}_2 }' class='latex' /> for all test functions <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' />. By the Reisz Representation Theorem, for each <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmu+%5Cin+M%28%7B%5Cmathbb+R%7D%5Ed%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mu &#92;in M({&#92;mathbb R}^d)}' title='{&#92;mu &#92;in M({&#92;mathbb R}^d)}' class='latex' /> (the space of all Radon measures on <img src='http://s0.wp.com/latex.php?latex=%7B%7B%5Cmathbb+R%7D%5Ed%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{{&#92;mathbb R}^d}' title='{{&#92;mathbb R}^d}' class='latex' />), if we let <img src='http://s0.wp.com/latex.php?latex=%7BI_%5Cmu%28h%29%3D+%5Cint+h+d%5Cmu%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{I_&#92;mu(h)= &#92;int h d&#92;mu}' title='{I_&#92;mu(h)= &#92;int h d&#92;mu}' class='latex' />, then the map <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmu+%5Crightarrow+I_%5Cmu%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mu &#92;rightarrow I_&#92;mu}' title='{&#92;mu &#92;rightarrow I_&#92;mu}' class='latex' /> is an isometric isomorphism between <img src='http://s0.wp.com/latex.php?latex=%7BM%28%7B%5Cmathbb+R%7D%5Ed%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{M({&#92;mathbb R}^d)}' title='{M({&#92;mathbb R}^d)}' class='latex' /> and <img src='http://s0.wp.com/latex.php?latex=%7BC_0%28%7B%5Cmathbb+R%7D%5Ed%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C_0({&#92;mathbb R}^d)}' title='{C_0({&#92;mathbb R}^d)}' class='latex' />. Since <img src='http://s0.wp.com/latex.php?latex=%7BC_c%5E%5Cinfty%28%7B%5Cmathbb+R%7D%5Ed%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C_c^&#92;infty({&#92;mathbb R}^d)}' title='{C_c^&#92;infty({&#92;mathbb R}^d)}' class='latex' /> is a subspace of <img src='http://s0.wp.com/latex.php?latex=%7BC_0%28%7B%5Cmathbb+R%7D%5Ed%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C_0({&#92;mathbb R}^d)}' title='{C_0({&#92;mathbb R}^d)}' class='latex' />, we have <img src='http://s0.wp.com/latex.php?latex=%7BI_%7B%5Coverline%7B%5Cmu%7D_1%7D%28f%29%3DI_%7B%5Coverline%7B%5Cmu%7D_2%7D%28f%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{I_{&#92;overline{&#92;mu}_1}(f)=I_{&#92;overline{&#92;mu}_2}(f)}' title='{I_{&#92;overline{&#92;mu}_1}(f)=I_{&#92;overline{&#92;mu}_2}(f)}' class='latex' /> on <img src='http://s0.wp.com/latex.php?latex=%7BC_c%5E%5Cinfty%28%7B%5Cmathbb+R%7D%5Ed%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C_c^&#92;infty({&#92;mathbb R}^d)}' title='{C_c^&#92;infty({&#92;mathbb R}^d)}' class='latex' />.</p>
<p>
Now according to Part iv. of Exercise 1, <img src='http://s0.wp.com/latex.php?latex=%7BC_c%5E%5Cinfty%28%7B%5Cmathbb+R%7D%5Ed%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C_c^&#92;infty({&#92;mathbb R}^d)}' title='{C_c^&#92;infty({&#92;mathbb R}^d)}' class='latex' /> is a dense subset of <img src='http://s0.wp.com/latex.php?latex=%7BC_0%28%7B%5Cmathbb+R%7D%5Ed%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C_0({&#92;mathbb R}^d)}' title='{C_0({&#92;mathbb R}^d)}' class='latex' /> in the uniform topology. Thus <img src='http://s0.wp.com/latex.php?latex=%7BI_%7B%5Coverline%7B%5Cmu%7D_1%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{I_{&#92;overline{&#92;mu}_1}}' title='{I_{&#92;overline{&#92;mu}_1}}' class='latex' /> and <img src='http://s0.wp.com/latex.php?latex=%7BI_%7B%5Coverline%7B%5Cmu%7D_1%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{I_{&#92;overline{&#92;mu}_1}}' title='{I_{&#92;overline{&#92;mu}_1}}' class='latex' /> are continuous linear functionals on <img src='http://s0.wp.com/latex.php?latex=%7BC_0%28%7B%5Cmathbb+R%7D%5Ed%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C_0({&#92;mathbb R}^d)}' title='{C_0({&#92;mathbb R}^d)}' class='latex' /> that agree on the dense subset <img src='http://s0.wp.com/latex.php?latex=%7BC_C%5E%5Cinfty%28%7B%5Cmathbb+R%7D%5Ed%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C_C^&#92;infty({&#92;mathbb R}^d)}' title='{C_C^&#92;infty({&#92;mathbb R}^d)}' class='latex' />. Therefore <img src='http://s0.wp.com/latex.php?latex=%7BI_%7B%5Coverline%7B%5Cmu%7D_1%7D%3DI_%7B%5Coverline%7B%5Cmu%7D_2%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{I_{&#92;overline{&#92;mu}_1}=I_{&#92;overline{&#92;mu}_2}}' title='{I_{&#92;overline{&#92;mu}_1}=I_{&#92;overline{&#92;mu}_2}}' class='latex' /> on all of <img src='http://s0.wp.com/latex.php?latex=%7BC_0%28%7B%5Cmathbb+R%7D%5Ed%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C_0({&#92;mathbb R}^d)}' title='{C_0({&#92;mathbb R}^d)}' class='latex' />.</p>
<p>
Our map between <img src='http://s0.wp.com/latex.php?latex=%7BM%28%7B%5Cmathbb+R%7D%5Ed%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{M({&#92;mathbb R}^d)}' title='{M({&#92;mathbb R}^d)}' class='latex' /> and <img src='http://s0.wp.com/latex.php?latex=%7BC_0%28%7B%5Cmathbb+R%7D%5Ed%29%5E%2A%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C_0({&#92;mathbb R}^d)^*}' title='{C_0({&#92;mathbb R}^d)^*}' class='latex' /> is an isomorphism, and thus <img src='http://s0.wp.com/latex.php?latex=%7B%5Coverline%7B%5Cmu%7D_1%3D%5Coverline%7B%5Cmu%7D_2%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;overline{&#92;mu}_1=&#92;overline{&#92;mu}_2}' title='{&#92;overline{&#92;mu}_1=&#92;overline{&#92;mu}_2}' class='latex' />. We see <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmu_1%3D%5Cmu_2%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mu_1=&#92;mu_2}' title='{&#92;mu_1=&#92;mu_2}' class='latex' />. The identification of Radon measures with their induced distributions is injective, and therefore, the identification of locally integrable functions with their distributions is also injective.</p>
<p>
<p><b> Exercise 10 </b></p>
<p><p>
Let <img src='http://s0.wp.com/latex.php?latex=%7B%5Cphi_n%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;phi_n}' title='{&#92;phi_n}' class='latex' /> be a sequence of approximations to the identity. Then each <img src='http://s0.wp.com/latex.php?latex=%7B%5Cphi_n%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;phi_n}' title='{&#92;phi_n}' class='latex' /> induces a distribution (which we&#8217;ll also denote <img src='http://s0.wp.com/latex.php?latex=%7B%5Cphi_n%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;phi_n)}' title='{&#92;phi_n)}' class='latex' />, defined on each test function <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' /> by <img src='http://s0.wp.com/latex.php?latex=%7B%5Clangle+f%2C+%5Cphi_n+%5Crangle+%3D+%5Cint+f+%5Cphi_n%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;langle f, &#92;phi_n &#92;rangle = &#92;int f &#92;phi_n}' title='{&#92;langle f, &#92;phi_n &#92;rangle = &#92;int f &#92;phi_n}' class='latex' />. Note that since each <img src='http://s0.wp.com/latex.php?latex=%7B%5Cphi_n%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;phi_n}' title='{&#92;phi_n}' class='latex' /> is non-negative (and hence real), <img src='http://s0.wp.com/latex.php?latex=%7B%5Coverline%7B%5Cphi_n%7D%3D%7C%5Cphi_n%7C%3D%5Cphi_n%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;overline{&#92;phi_n}=|&#92;phi_n|=&#92;phi_n}' title='{&#92;overline{&#92;phi_n}=|&#92;phi_n|=&#92;phi_n}' class='latex' /> for each <img src='http://s0.wp.com/latex.php?latex=%7Bn%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{n}' title='{n}' class='latex' />.</p>
<p>
Fix any test function <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' />, and <img src='http://s0.wp.com/latex.php?latex=%7B%5Cepsilon+%3E0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;epsilon &gt;0}' title='{&#92;epsilon &gt;0}' class='latex' />. Now <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' /> is continuous, particularly at 0. Thus, there exists a <img src='http://s0.wp.com/latex.php?latex=%7B%5Cdelta%3E0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;delta&gt;0}' title='{&#92;delta&gt;0}' class='latex' /> such that <img src='http://s0.wp.com/latex.php?latex=%7B%7Cf%28x%29-f%280%29%7C%3C%5Cfrac%7B%5Cepsilon%7D%7B2%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{|f(x)-f(0)|&lt;&#92;frac{&#92;epsilon}{2}}' title='{|f(x)-f(0)|&lt;&#92;frac{&#92;epsilon}{2}}' class='latex' /> whenever <img src='http://s0.wp.com/latex.php?latex=%7B%7Cx%7C%3C%5Cdelta%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{|x|&lt;&#92;delta}' title='{|x|&lt;&#92;delta}' class='latex' />.</p>
<p>
<img src='http://s0.wp.com/latex.php?latex=%7Bg%28x%29%3Df%28x%29-f%280%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g(x)=f(x)-f(0)}' title='{g(x)=f(x)-f(0)}' class='latex' /> is bounded. Now use the same <img src='http://s0.wp.com/latex.php?latex=%7B%5Cdelta%3E0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;delta&gt;0}' title='{&#92;delta&gt;0}' class='latex' /> as above. Then for any <img src='http://s0.wp.com/latex.php?latex=%7Bn%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{n}' title='{n}' class='latex' />,
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Cbegin%7Barray%7D%7Brcl%7D++%7C%5Cint_%7B%7Cx%7C%5Cgeq+%5Cdelta%7D+%28f%28x%29-f%280%29+%5Cphi_n%28x%29dx%7C+%26+%3D+%5Cint_E+%7Cg%28x%29+%5Cphi_n%28x%29%7C+dx+%5Cleq+%5C%7Cg%5C%7C+%5Cint_%7B%7Cx%7C%5Cgeq+%5Cdelta%7D+%5Cphi_n%28x%29+dx+%5Cend%7Barray%7D+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;begin{array}{rcl}  |&#92;int_{|x|&#92;geq &#92;delta} (f(x)-f(0) &#92;phi_n(x)dx| &amp; = &#92;int_E |g(x) &#92;phi_n(x)| dx &#92;leq &#92;|g&#92;| &#92;int_{|x|&#92;geq &#92;delta} &#92;phi_n(x) dx &#92;end{array} ' title='&#92;displaystyle  &#92;begin{array}{rcl}  |&#92;int_{|x|&#92;geq &#92;delta} (f(x)-f(0) &#92;phi_n(x)dx| &amp; = &#92;int_E |g(x) &#92;phi_n(x)| dx &#92;leq &#92;|g&#92;| &#92;int_{|x|&#92;geq &#92;delta} &#92;phi_n(x) dx &#92;end{array} ' class='latex' /></p>
<p>
<img src='http://s0.wp.com/latex.php?latex=%7B%5Cphi_n%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;phi_n}' title='{&#92;phi_n}' class='latex' /> is a sequence of approximations to the identity, and therefore by definition, <img src='http://s0.wp.com/latex.php?latex=%7B%5Clim_%7Bn+%5Crightarrow+%5Cinfty%7D+%5Cint_%7B%7Cx%7C%5Cgeq+%5Cdelta%7D+%5Cphi_n%28x%29+%3D0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;lim_{n &#92;rightarrow &#92;infty} &#92;int_{|x|&#92;geq &#92;delta} &#92;phi_n(x) =0}' title='{&#92;lim_{n &#92;rightarrow &#92;infty} &#92;int_{|x|&#92;geq &#92;delta} &#92;phi_n(x) =0}' class='latex' />. Thus, there exists an <img src='http://s0.wp.com/latex.php?latex=%7BN%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{N}' title='{N}' class='latex' /> such that if <img src='http://s0.wp.com/latex.php?latex=%7Bn%3EN%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{n&gt;N}' title='{n&gt;N}' class='latex' />, then we have <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7Cg%5C%7C+%5Cint_%7B%7Cx%7C%5Cgeq+%5Cdelta%7D+%5Cphi_n%28x%29+dx+%3C+%5Cfrac%7B%5Cepsilon%7D%7B2%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;|g&#92;| &#92;int_{|x|&#92;geq &#92;delta} &#92;phi_n(x) dx &lt; &#92;frac{&#92;epsilon}{2}}' title='{&#92;|g&#92;| &#92;int_{|x|&#92;geq &#92;delta} &#92;phi_n(x) dx &lt; &#92;frac{&#92;epsilon}{2}}' class='latex' />.</p>
<p>
Then given any <img src='http://s0.wp.com/latex.php?latex=%7Bn%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{n}' title='{n}' class='latex' /> greater than the above <img src='http://s0.wp.com/latex.php?latex=%7BN%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{N}' title='{N}' class='latex' />, we see
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Cbegin%7Barray%7D%7Brcl%7D++%7C%5Cint+f%28x%29+%5Cphi_n%28x%29dx-+f%280%29%7C+%26+%3D+%7C%5Cint+f%28x%29+%5Cphi_n%28x%29dx-+f%280%29%5Cint+%5Cphi_n%28x%29dx%7C+%3D+%7C%5Cint+%28f%28x%29-f%280%29%29+%5Cphi_n%28x%29dx%7C+%5C%5C+%26+%5Cleq+%7C%5Cint_%7B%7Cx%7C%3C%5Cdelta%7D+%28f%28x%29-f%280%29%29+%5Cphi_n%28x%29dx%7C+%2B+%7C%5Cint_%7B%7Cx%7C%5Cgeq%5Cdelta%7D+%28f%28x%29-f%280%29%29+%5Cphi_n%28x%29dx%7C+%5C%5C+%26+%5Cleq+%5Cint_%7B%7Cx%7C%3C%5Cdelta%7D+%7Cf%28x%29-f%280%29%7C%7C+%5Cphi_n%28x%29%7Cdx+%2B+%5Cint_%7B%7Cx%7C%5Cgeq%5Cdelta%7D+%7Cf%28x%29-f%280%29%7C+%7C%5Cphi_n%28x%29%7Cdx+%5C%5C+%26+%3C+%5Cint_%7B%7Cx%7C%3C%5Cdelta%7D+%5Cfrac%7B%5Cepsilon%7D%7B2%7D+%5Cphi_n%28x%29dx+%2B+%5Cint_%7B%7Cx%7C%5Cgeq%5Cdelta%7D+%5C%7Cg%5C%7C+%5Cphi_n%28x%29dx+%5C%5C+%26+%5Cleq+%5Cfrac%7B%5Cepsilon%7D%7B2%7D+%5Cint_%7B%7Cx%7C%3C%5Cdelta%7D+%5Cphi_n%28x%29dx+%2B+%5C%7Cg%5C%7C+%5Cint_%7B%7Cx%7C%5Cgeq%5Cdelta%7D+%5Cphi_n%28x%29dx+%5C%5C+%26+%5Cleq+%5Cfrac%7B%5Cepsilon%7D%7B2%7D+%5Cint%5Cphi_n%28x%29dx+%2B+%5Cfrac%7B%5Cepsilon%7D%7B2%7D+%3D+%5Cfrac%7B%5Cepsilon%7D%7B2%7D%2B%5Cfrac%7B%5Cepsilon%7D%7B2%7D+%5Cend%7Barray%7D+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;begin{array}{rcl}  |&#92;int f(x) &#92;phi_n(x)dx- f(0)| &amp; = |&#92;int f(x) &#92;phi_n(x)dx- f(0)&#92;int &#92;phi_n(x)dx| = |&#92;int (f(x)-f(0)) &#92;phi_n(x)dx| &#92;&#92; &amp; &#92;leq |&#92;int_{|x|&lt;&#92;delta} (f(x)-f(0)) &#92;phi_n(x)dx| + |&#92;int_{|x|&#92;geq&#92;delta} (f(x)-f(0)) &#92;phi_n(x)dx| &#92;&#92; &amp; &#92;leq &#92;int_{|x|&lt;&#92;delta} |f(x)-f(0)|| &#92;phi_n(x)|dx + &#92;int_{|x|&#92;geq&#92;delta} |f(x)-f(0)| |&#92;phi_n(x)|dx &#92;&#92; &amp; &lt; &#92;int_{|x|&lt;&#92;delta} &#92;frac{&#92;epsilon}{2} &#92;phi_n(x)dx + &#92;int_{|x|&#92;geq&#92;delta} &#92;|g&#92;| &#92;phi_n(x)dx &#92;&#92; &amp; &#92;leq &#92;frac{&#92;epsilon}{2} &#92;int_{|x|&lt;&#92;delta} &#92;phi_n(x)dx + &#92;|g&#92;| &#92;int_{|x|&#92;geq&#92;delta} &#92;phi_n(x)dx &#92;&#92; &amp; &#92;leq &#92;frac{&#92;epsilon}{2} &#92;int&#92;phi_n(x)dx + &#92;frac{&#92;epsilon}{2} = &#92;frac{&#92;epsilon}{2}+&#92;frac{&#92;epsilon}{2} &#92;end{array} ' title='&#92;displaystyle  &#92;begin{array}{rcl}  |&#92;int f(x) &#92;phi_n(x)dx- f(0)| &amp; = |&#92;int f(x) &#92;phi_n(x)dx- f(0)&#92;int &#92;phi_n(x)dx| = |&#92;int (f(x)-f(0)) &#92;phi_n(x)dx| &#92;&#92; &amp; &#92;leq |&#92;int_{|x|&lt;&#92;delta} (f(x)-f(0)) &#92;phi_n(x)dx| + |&#92;int_{|x|&#92;geq&#92;delta} (f(x)-f(0)) &#92;phi_n(x)dx| &#92;&#92; &amp; &#92;leq &#92;int_{|x|&lt;&#92;delta} |f(x)-f(0)|| &#92;phi_n(x)|dx + &#92;int_{|x|&#92;geq&#92;delta} |f(x)-f(0)| |&#92;phi_n(x)|dx &#92;&#92; &amp; &lt; &#92;int_{|x|&lt;&#92;delta} &#92;frac{&#92;epsilon}{2} &#92;phi_n(x)dx + &#92;int_{|x|&#92;geq&#92;delta} &#92;|g&#92;| &#92;phi_n(x)dx &#92;&#92; &amp; &#92;leq &#92;frac{&#92;epsilon}{2} &#92;int_{|x|&lt;&#92;delta} &#92;phi_n(x)dx + &#92;|g&#92;| &#92;int_{|x|&#92;geq&#92;delta} &#92;phi_n(x)dx &#92;&#92; &amp; &#92;leq &#92;frac{&#92;epsilon}{2} &#92;int&#92;phi_n(x)dx + &#92;frac{&#92;epsilon}{2} = &#92;frac{&#92;epsilon}{2}+&#92;frac{&#92;epsilon}{2} &#92;end{array} ' class='latex' /></p>
<p>
Therefore, for any test function <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' />, <img src='http://s0.wp.com/latex.php?latex=%7B%5Clim_%7Bn+%5Crightarrow+%5Cinfty%7D+%5Cint+f%28x%29%5Cphi_n%28x%29dx%3Df%280%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;lim_{n &#92;rightarrow &#92;infty} &#92;int f(x)&#92;phi_n(x)dx=f(0)}' title='{&#92;lim_{n &#92;rightarrow &#92;infty} &#92;int f(x)&#92;phi_n(x)dx=f(0)}' class='latex' />. Thus, <img src='http://s0.wp.com/latex.php?latex=%7B%5Clim_%7Bn%5Crightarrow%5Cinfty%7D+%5Clangle+f%2C+%5Cphi_n+%5Crangle+%3D+%5Clangle+f%2C+%5Cdelta+%5Crangle%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;lim_{n&#92;rightarrow&#92;infty} &#92;langle f, &#92;phi_n &#92;rangle = &#92;langle f, &#92;delta &#92;rangle}' title='{&#92;lim_{n&#92;rightarrow&#92;infty} &#92;langle f, &#92;phi_n &#92;rangle = &#92;langle f, &#92;delta &#92;rangle}' class='latex' /> for each test function <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7B%5Cphi_n%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;phi_n}' title='{&#92;phi_n}' class='latex' /> converges in the sense of distributions to the Dirac distribution <img src='http://s0.wp.com/latex.php?latex=%7B%5Cdelta%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;delta}' title='{&#92;delta}' class='latex' />.</p>
<p>
<p><b> Exercise 16 </b></p>
<p><p>
The first part is trivial. For any test function <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' />, we see
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Clangle+f%2C+%5Cdelta+x+%5Crangle+%3D+%5Clangle+%5Coverline%7Bx%7D+f+%2C+%5Cdelta+%5Crangle+%3D+%5Clangle+xf%2C+%5Cdelta+%5Crangle+%3D+0+f%280%29+%3D0+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;langle f, &#92;delta x &#92;rangle = &#92;langle &#92;overline{x} f , &#92;delta &#92;rangle = &#92;langle xf, &#92;delta &#92;rangle = 0 f(0) =0 ' title='&#92;displaystyle  &#92;langle f, &#92;delta x &#92;rangle = &#92;langle &#92;overline{x} f , &#92;delta &#92;rangle = &#92;langle xf, &#92;delta &#92;rangle = 0 f(0) =0 ' class='latex' /></p>
<p> Therefore, <img src='http://s0.wp.com/latex.php?latex=%7B%5Cdelta+x%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;delta x}' title='{&#92;delta x}' class='latex' /> is identically 0.</p>
<p>
The converse is not as straight forward. Fix a test function <img src='http://s0.wp.com/latex.php?latex=%7B%5Cpsi%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;psi}' title='{&#92;psi}' class='latex' /> such that <img src='http://s0.wp.com/latex.php?latex=%7B%5Cpsi%280%29%3D1%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;psi(0)=1}' title='{&#92;psi(0)=1}' class='latex' />. Now for any test function <img src='http://s0.wp.com/latex.php?latex=%7Bg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g}' title='{g}' class='latex' />, consider <img src='http://s0.wp.com/latex.php?latex=%7BG%28x%29%3D+g%280%29%2B+x+%5Cint_0%5E1+g%5E%5Cprime%28xt%29+dt%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{G(x)= g(0)+ x &#92;int_0^1 g^&#92;prime(xt) dt}' title='{G(x)= g(0)+ x &#92;int_0^1 g^&#92;prime(xt) dt}' class='latex' />. It&#8217;s immediate that <img src='http://s0.wp.com/latex.php?latex=%7BG%280%29%3Dg%280%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{G(0)=g(0)}' title='{G(0)=g(0)}' class='latex' />, and if <img src='http://s0.wp.com/latex.php?latex=%7Bx+%5Cneq+0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x &#92;neq 0}' title='{x &#92;neq 0}' class='latex' />, then
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++G%28x%29%3Dg%280%29%2Bx+%5Cint_0%5E1+g%5E%5Cprime%28tx%29+dt+%3D+g%280%29%2B+x+%5Cint_0%5Ex+%5Cfrac%7Bg%5E%5Cprime%28u%29%7D%7Bx%7D+du+%3D+g%280%29+%2B+%5Cfrac%7Bx%7D%7Bx%7D%28g%28x%29-g%280%29%29%3Dg%28x%29+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  G(x)=g(0)+x &#92;int_0^1 g^&#92;prime(tx) dt = g(0)+ x &#92;int_0^x &#92;frac{g^&#92;prime(u)}{x} du = g(0) + &#92;frac{x}{x}(g(x)-g(0))=g(x) ' title='&#92;displaystyle  G(x)=g(0)+x &#92;int_0^1 g^&#92;prime(tx) dt = g(0)+ x &#92;int_0^x &#92;frac{g^&#92;prime(u)}{x} du = g(0) + &#92;frac{x}{x}(g(x)-g(0))=g(x) ' class='latex' /></p>
<p> Therefore <img src='http://s0.wp.com/latex.php?latex=%7BG%3Dg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{G=g}' title='{G=g}' class='latex' />.</p>
<p>
Now pick any test function <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' />.
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Clangle+f%2C+%5Clambda+%5Crangle+%3D+%5Clangle+f-f%280%29%5Cpsi%2Bf%280%29%5Cpsi+%5Crangle+%3D+%5Clangle+f-f%280%29%5Cpsi%2C+%5Clambda+%5Crangle+%2B+f%280%29+%5Clangle+%5Cpsi%2C+%5Clambda+%5Crangle+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;langle f, &#92;lambda &#92;rangle = &#92;langle f-f(0)&#92;psi+f(0)&#92;psi &#92;rangle = &#92;langle f-f(0)&#92;psi, &#92;lambda &#92;rangle + f(0) &#92;langle &#92;psi, &#92;lambda &#92;rangle ' title='&#92;displaystyle  &#92;langle f, &#92;lambda &#92;rangle = &#92;langle f-f(0)&#92;psi+f(0)&#92;psi &#92;rangle = &#92;langle f-f(0)&#92;psi, &#92;lambda &#92;rangle + f(0) &#92;langle &#92;psi, &#92;lambda &#92;rangle ' class='latex' /></p>
<p>
Consider <img src='http://s0.wp.com/latex.php?latex=%7Bf-f%280%29%5Cpsi%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f-f(0)&#92;psi}' title='{f-f(0)&#92;psi}' class='latex' />. Let <img src='http://s0.wp.com/latex.php?latex=%7BH%28x%29%3D%5Cint_0%5E1+f%5E%5Cprime%28xt%29-f%280%29%5Cpsi%5E%5Cprime%28xt%29dt%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{H(x)=&#92;int_0^1 f^&#92;prime(xt)-f(0)&#92;psi^&#92;prime(xt)dt}' title='{H(x)=&#92;int_0^1 f^&#92;prime(xt)-f(0)&#92;psi^&#92;prime(xt)dt}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7BH%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{H}' title='{H}' class='latex' /> is a test function, and from our previous calculation, <img src='http://s0.wp.com/latex.php?latex=%7Bf%28x%29-f%280%29%5Cpsi%28x%29%3Dx+H%28x%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f(x)-f(0)&#92;psi(x)=x H(x)}' title='{f(x)-f(0)&#92;psi(x)=x H(x)}' class='latex' />. Therefore
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Clangle+f-f%280%29%5Cpsi%2C+%5Clambda+%5Crangle+%3D+%5Clangle+x+H%2C+%5Clambda+%5Crangle+%3D+%5Clangle+H%2C+%5Clambda+x+%5Crangle+%3D0+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;langle f-f(0)&#92;psi, &#92;lambda &#92;rangle = &#92;langle x H, &#92;lambda &#92;rangle = &#92;langle H, &#92;lambda x &#92;rangle =0 ' title='&#92;displaystyle  &#92;langle f-f(0)&#92;psi, &#92;lambda &#92;rangle = &#92;langle x H, &#92;lambda &#92;rangle = &#92;langle H, &#92;lambda x &#92;rangle =0 ' class='latex' /></p>
<p>
We combine our two calculations, and we see
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Clangle+f%2C+%5Clambda+%5Crangle+%3D+%5Clangle+f-f%280%29%5Cpsi%2C+%5Clambda+%5Crangle+%2B+f%280%29+%5Clangle+%5Cpsi%2C+%5Clambda+%5Crangle+%3D+0+%2B+%5Clangle+%5Clangle+%5Cpsi%2C+%5Clambda+%5Crangle+f%2C+%5Cdelta+%5Crangle+%3D+%5Clangle+f%2C+%5Coverline%7B%5Clangle+%5Cpsi%2C+%5Clambda+%5Crangle%7D+%5Cdelta+%5Crangle+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;langle f, &#92;lambda &#92;rangle = &#92;langle f-f(0)&#92;psi, &#92;lambda &#92;rangle + f(0) &#92;langle &#92;psi, &#92;lambda &#92;rangle = 0 + &#92;langle &#92;langle &#92;psi, &#92;lambda &#92;rangle f, &#92;delta &#92;rangle = &#92;langle f, &#92;overline{&#92;langle &#92;psi, &#92;lambda &#92;rangle} &#92;delta &#92;rangle ' title='&#92;displaystyle  &#92;langle f, &#92;lambda &#92;rangle = &#92;langle f-f(0)&#92;psi, &#92;lambda &#92;rangle + f(0) &#92;langle &#92;psi, &#92;lambda &#92;rangle = 0 + &#92;langle &#92;langle &#92;psi, &#92;lambda &#92;rangle f, &#92;delta &#92;rangle = &#92;langle f, &#92;overline{&#92;langle &#92;psi, &#92;lambda &#92;rangle} &#92;delta &#92;rangle ' class='latex' /></p>
<p> Let <img src='http://s0.wp.com/latex.php?latex=%7BC%3D%5Coverline%7B%5Clangle+%5Cpsi%2C+%5Clambda+%5Crangle%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C=&#92;overline{&#92;langle &#92;psi, &#92;lambda &#92;rangle}}' title='{C=&#92;overline{&#92;langle &#92;psi, &#92;lambda &#92;rangle}}' class='latex' />, then since the above equality holds for each test function <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' />. We have that <img src='http://s0.wp.com/latex.php?latex=%7B%5Clambda+%3D+C+%5Cdelta%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;lambda = C &#92;delta}' title='{&#92;lambda = C &#92;delta}' class='latex' />.</p>
<p>
<p><b> Exercise 18 </b></p>
<p><p>
We&#8217;re working in <img src='http://s0.wp.com/latex.php?latex=%7B%7B%5Cmathbb+R%7D%5Ed%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{{&#92;mathbb R}^d}' title='{{&#92;mathbb R}^d}' class='latex' />. Pick any distribution <img src='http://s0.wp.com/latex.php?latex=%7B%5Clambda%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;lambda}' title='{&#92;lambda}' class='latex' />. For each positive integer <img src='http://s0.wp.com/latex.php?latex=%7Bn%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{n}' title='{n}' class='latex' />, let <img src='http://s0.wp.com/latex.php?latex=%7BK_n+%3D+%5B-n%2Cn%5D%5Ed%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{K_n = [-n,n]^d}' title='{K_n = [-n,n]^d}' class='latex' />, and let <img src='http://s0.wp.com/latex.php?latex=%7BU_n%3D%28-2n%2C2n%29%5Ed%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U_n=(-2n,2n)^d}' title='{U_n=(-2n,2n)^d}' class='latex' />. By Part iii. of Exercise 1, there exists a test function <img src='http://s0.wp.com/latex.php?latex=%7B%5Ceta_n%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;eta_n}' title='{&#92;eta_n}' class='latex' /> such that <img src='http://s0.wp.com/latex.php?latex=%7B%5Ceta_n%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;eta_n}' title='{&#92;eta_n}' class='latex' /> is 1 on <img src='http://s0.wp.com/latex.php?latex=%7BK_n%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{K_n}' title='{K_n}' class='latex' /> and vanishes outside <img src='http://s0.wp.com/latex.php?latex=%7BU_n%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U_n}' title='{U_n}' class='latex' />. We claim that for each <img src='http://s0.wp.com/latex.php?latex=%7Bn%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{n}' title='{n}' class='latex' />, the distribution <img src='http://s0.wp.com/latex.php?latex=%7B%5Clambda+%5Ceta_n%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;lambda &#92;eta_n}' title='{&#92;lambda &#92;eta_n}' class='latex' /> is compactly supported, and the <img src='http://s0.wp.com/latex.php?latex=%7B%5Clambda+%5Ceta_n%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;lambda &#92;eta_n}' title='{&#92;lambda &#92;eta_n}' class='latex' /> converge to <img src='http://s0.wp.com/latex.php?latex=%7B%5Clambda%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;lambda}' title='{&#92;lambda}' class='latex' /> in the sense of distributions.</p>
<p>
Consider <img src='http://s0.wp.com/latex.php?latex=%7B%5Clambda+%5Ceta_n%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;lambda &#92;eta_n}' title='{&#92;lambda &#92;eta_n}' class='latex' />. Suppose the test function <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' /> vanishes on <img src='http://s0.wp.com/latex.php?latex=%7B%5Coverline%7BU%7D_n%3D%5B-2n%2C2n%5D%5Ed%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;overline{U}_n=[-2n,2n]^d}' title='{&#92;overline{U}_n=[-2n,2n]^d}' class='latex' />. Now <img src='http://s0.wp.com/latex.php?latex=%7B%5Clangle+f%2C+%5Clambda+%5Ceta_n+%5Crangle%3D+%5Clangle+f+%5Coverline%7B%5Ceta%7D_n%2C+%5Clambda+%5Crangle%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;langle f, &#92;lambda &#92;eta_n &#92;rangle= &#92;langle f &#92;overline{&#92;eta}_n, &#92;lambda &#92;rangle}' title='{&#92;langle f, &#92;lambda &#92;eta_n &#92;rangle= &#92;langle f &#92;overline{&#92;eta}_n, &#92;lambda &#92;rangle}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' /> vanishes on <img src='http://s0.wp.com/latex.php?latex=%7B%5Coverline%7BU%7D_n%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;overline{U}_n}' title='{&#92;overline{U}_n}' class='latex' />, so <img src='http://s0.wp.com/latex.php?latex=%7Bf+%5Coverline%7B%5Ceta_n%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f &#92;overline{&#92;eta_n}}' title='{f &#92;overline{&#92;eta_n}}' class='latex' /> must as well. <img src='http://s0.wp.com/latex.php?latex=%7B%5Coverline%7B%5Ceta%7D_n%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;overline{&#92;eta}_n}' title='{&#92;overline{&#92;eta}_n}' class='latex' /> vanishes outside <img src='http://s0.wp.com/latex.php?latex=%7BU_n%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U_n}' title='{U_n}' class='latex' />, so <img src='http://s0.wp.com/latex.php?latex=%7Bf+%5Coverline%7B%5Ceta_n%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f &#92;overline{&#92;eta_n}}' title='{f &#92;overline{&#92;eta_n}}' class='latex' /> must vanish outside <img src='http://s0.wp.com/latex.php?latex=%7BU_n%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U_n}' title='{U_n}' class='latex' /> as well. So <img src='http://s0.wp.com/latex.php?latex=%7Bf+%5Coverline%7B%5Ceta%7D_n%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f &#92;overline{&#92;eta}_n}' title='{f &#92;overline{&#92;eta}_n}' class='latex' /> is identically 0 on all of <img src='http://s0.wp.com/latex.php?latex=%7B%7B%5Cmathbb+R%7D%5Ed%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{{&#92;mathbb R}^d}' title='{{&#92;mathbb R}^d}' class='latex' />. Distributions are linear functionals, and thus <img src='http://s0.wp.com/latex.php?latex=%7B%5Clangle+f+%5Coverline%7B%5Ceta%7D_n%2C+%5Clambda+%5Crangle+%3D+%5Clangle+0%2C%5Clambda+%5Crangle+%3D0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;langle f &#92;overline{&#92;eta}_n, &#92;lambda &#92;rangle = &#92;langle 0,&#92;lambda &#92;rangle =0}' title='{&#92;langle f &#92;overline{&#92;eta}_n, &#92;lambda &#92;rangle = &#92;langle 0,&#92;lambda &#92;rangle =0}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7B%5Clangle+f%2C+%5Clambda+%5Ceta_n+%5Crangle+%3D0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;langle f, &#92;lambda &#92;eta_n &#92;rangle =0}' title='{&#92;langle f, &#92;lambda &#92;eta_n &#92;rangle =0}' class='latex' /> for each <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' /> that vanishes on <img src='http://s0.wp.com/latex.php?latex=%7B%5Coverline%7BU%7D_n%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;overline{U}_n}' title='{&#92;overline{U}_n}' class='latex' />. The distribution <img src='http://s0.wp.com/latex.php?latex=%7B%5Clambda+%5Ceta_n%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;lambda &#92;eta_n}' title='{&#92;lambda &#92;eta_n}' class='latex' /> is supported on <img src='http://s0.wp.com/latex.php?latex=%7B%5Coverline%7BU%7D_n%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;overline{U}_n}' title='{&#92;overline{U}_n}' class='latex' />. The support of <img src='http://s0.wp.com/latex.php?latex=%7B%5Clambda+%5Ceta_n%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;lambda &#92;eta_n}' title='{&#92;lambda &#92;eta_n}' class='latex' /> is thus a closed subset of the compact set <img src='http://s0.wp.com/latex.php?latex=%7B%5Coverline%7BU%7D_n%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;overline{U}_n}' title='{&#92;overline{U}_n}' class='latex' />, and therefore compact. Each <img src='http://s0.wp.com/latex.php?latex=%7B%5Clambda+%5Ceta_n%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;lambda &#92;eta_n}' title='{&#92;lambda &#92;eta_n}' class='latex' /> is a compactly supported distribution.</p>
<p>
Now given any test function <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' />, we claim <img src='http://s0.wp.com/latex.php?latex=%7B%5Clangle+f%2C+%5Clambda+%5Ceta_n+%5Crangle+%5Crightarrow+%5Clangle+f%2C+%5Clambda+%5Crangle+%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;langle f, &#92;lambda &#92;eta_n &#92;rangle &#92;rightarrow &#92;langle f, &#92;lambda &#92;rangle }' title='{&#92;langle f, &#92;lambda &#92;eta_n &#92;rangle &#92;rightarrow &#92;langle f, &#92;lambda &#92;rangle }' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' /> is compactly supported. So there exists a <img src='http://s0.wp.com/latex.php?latex=%7BN%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{N}' title='{N}' class='latex' /> such that <img src='http://s0.wp.com/latex.php?latex=%7BK_N%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{K_N}' title='{K_N}' class='latex' /> contains the support of <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' />. Then for any <img src='http://s0.wp.com/latex.php?latex=%7Bn+%5Cgeq+N%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{n &#92;geq N}' title='{n &#92;geq N}' class='latex' />, consider <img src='http://s0.wp.com/latex.php?latex=%7Bf+%5Coverline%7B%5Ceta%7D_n%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f &#92;overline{&#92;eta}_n}' title='{f &#92;overline{&#92;eta}_n}' class='latex' />. If <img src='http://s0.wp.com/latex.php?latex=%7Bx%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x}' title='{x}' class='latex' /> lies in the support of <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' />, then <img src='http://s0.wp.com/latex.php?latex=%7Bx%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x}' title='{x}' class='latex' /> also lies in <img src='http://s0.wp.com/latex.php?latex=%7BK_n%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{K_n}' title='{K_n}' class='latex' />, and therefore <img src='http://s0.wp.com/latex.php?latex=%7Bf%28x%29%5Coverline%7B%5Ceta%7D_n%28x%29%3Df%28x%29%5Coverline%7B1%7D%3Df%28x%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f(x)&#92;overline{&#92;eta}_n(x)=f(x)&#92;overline{1}=f(x)}' title='{f(x)&#92;overline{&#92;eta}_n(x)=f(x)&#92;overline{1}=f(x)}' class='latex' />. If <img src='http://s0.wp.com/latex.php?latex=%7Bx%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x}' title='{x}' class='latex' /> lies outside the support of <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' />, then <img src='http://s0.wp.com/latex.php?latex=%7Bf%28x%29%5Coverline%7B%5Ceta%7D_n%28x%29%3D0%3Df%28x%29+%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f(x)&#92;overline{&#92;eta}_n(x)=0=f(x) }' title='{f(x)&#92;overline{&#92;eta}_n(x)=0=f(x) }' class='latex' />. Therefore <img src='http://s0.wp.com/latex.php?latex=%7Bf%3Df%5Coverline%7B%5Ceta%7D_n%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f=f&#92;overline{&#92;eta}_n}' title='{f=f&#92;overline{&#92;eta}_n}' class='latex' /> for all <img src='http://s0.wp.com/latex.php?latex=%7Bn+%5Cgeq+N%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{n &#92;geq N}' title='{n &#92;geq N}' class='latex' />. Then for any <img src='http://s0.wp.com/latex.php?latex=%7Bn%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{n}' title='{n}' class='latex' /> greater than that same <img src='http://s0.wp.com/latex.php?latex=%7BN%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{N}' title='{N}' class='latex' />, we see <img src='http://s0.wp.com/latex.php?latex=%7B%5Clangle+f%2C+%5Clambda+%5Ceta_n+%5Crangle%3D+%5Clangle+f+%5Coverline%7B%5Ceta%7D_n%2C%5Clambda+%5Crangle+%3D+%5Clangle+f%2C+%5Clambda+%5Crangle%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;langle f, &#92;lambda &#92;eta_n &#92;rangle= &#92;langle f &#92;overline{&#92;eta}_n,&#92;lambda &#92;rangle = &#92;langle f, &#92;lambda &#92;rangle}' title='{&#92;langle f, &#92;lambda &#92;eta_n &#92;rangle= &#92;langle f &#92;overline{&#92;eta}_n,&#92;lambda &#92;rangle = &#92;langle f, &#92;lambda &#92;rangle}' class='latex' />. Therefore <img src='http://s0.wp.com/latex.php?latex=%7B%5Clangle+f%2C+%5Clambda+%5Ceta_n+%5Crangle+%5Crightarrow+%5Clangle+f%2C+%5Clambda+%5Crangle%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;langle f, &#92;lambda &#92;eta_n &#92;rangle &#92;rightarrow &#92;langle f, &#92;lambda &#92;rangle}' title='{&#92;langle f, &#92;lambda &#92;eta_n &#92;rangle &#92;rightarrow &#92;langle f, &#92;lambda &#92;rangle}' class='latex' />, and since our choice of <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' /> was arbitrary, this must hold for all test functions. The <img src='http://s0.wp.com/latex.php?latex=%7B%5Clambda+%5Ceta_n%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;lambda &#92;eta_n}' title='{&#92;lambda &#92;eta_n}' class='latex' /> converge to <img src='http://s0.wp.com/latex.php?latex=%7B%5Clambda%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;lambda}' title='{&#92;lambda}' class='latex' /> in the sense of distributions.</p>
<p>
Every distribution is the limit of a sequence of compactly supported distributions.</p>
<p>
<p><b> Exercise 20 </b></p>
<p> Without loss of generality, we&#8217;ll differentiate with respect to the <img src='http://s0.wp.com/latex.php?latex=%7Bi%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i}' title='{i}' class='latex' />-th variable, <img src='http://s0.wp.com/latex.php?latex=%7Bx_i%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x_i}' title='{x_i}' class='latex' />. Just apply the definition of the derivative to the left-hand side, and we see for each test function <img src='http://s0.wp.com/latex.php?latex=%7Bg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g}' title='{g}' class='latex' /> that
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Clangle+g%2C+%5Cfrac%7B%5Cpartial%7D%7B%5Cpartial+x_i%7D+%28%5Clambda+f%29+%5Crangle+%3D+-+%5Clangle+%5Cfrac%7B%5Cpartial+g%7D%7B%5Cpartial+x_i%7D+%2C+%5Clambda+f+%5Crangle+%3D+-+%5Clangle+%5Coverline%7Bf%7D+%5Cfrac%7B%5Cpartial+g%7D%7B%5Cpartial+x_i%7D%2C+%5Clambda+%5Crangle+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;langle g, &#92;frac{&#92;partial}{&#92;partial x_i} (&#92;lambda f) &#92;rangle = - &#92;langle &#92;frac{&#92;partial g}{&#92;partial x_i} , &#92;lambda f &#92;rangle = - &#92;langle &#92;overline{f} &#92;frac{&#92;partial g}{&#92;partial x_i}, &#92;lambda &#92;rangle ' title='&#92;displaystyle  &#92;langle g, &#92;frac{&#92;partial}{&#92;partial x_i} (&#92;lambda f) &#92;rangle = - &#92;langle &#92;frac{&#92;partial g}{&#92;partial x_i} , &#92;lambda f &#92;rangle = - &#92;langle &#92;overline{f} &#92;frac{&#92;partial g}{&#92;partial x_i}, &#92;lambda &#92;rangle ' class='latex' /></p>
<p>
Now apply the definition to each of the summands on the left-hand side. So for any test function <img src='http://s0.wp.com/latex.php?latex=%7Bg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g}' title='{g}' class='latex' />, we see
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Clangle+g%2C+%28%5Cfrac%7B%5Cpartial+%5Clambda%7D%7B%5Cpartial+x_i%7D%29+f+%5Crangle+%3D+%5Clangle+%5Coverline%7Bf%7D+g%2C+%5Cfrac%7B%5Cpartial+%5Clambda%7D%7B%5Cpartial+x_i%7D+%5Crangle+%3D+-+%5Clangle+%5Cfrac%7B%5Cpartial%7D%7B%5Cpartial+x_i%7D+%28%5Coverline%7Bf%7Dg%29%2C+%5Clambda+%5Crangle+%3D+-+%5Clangle+%5Cfrac%7B%5Cpartial+%5Coverline%7Bf%7D%7D%7B%5Cpartial+x_i%7D+g%2C+%5Clambda+%5Crangle+-+%5Clangle+%5Coverline%7Bf%7D+%5Cfrac%7B%5Cpartial+g%7D%7B%5Cpartial+x_i%7D%2C+%5Clambda+%5Crangle+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;langle g, (&#92;frac{&#92;partial &#92;lambda}{&#92;partial x_i}) f &#92;rangle = &#92;langle &#92;overline{f} g, &#92;frac{&#92;partial &#92;lambda}{&#92;partial x_i} &#92;rangle = - &#92;langle &#92;frac{&#92;partial}{&#92;partial x_i} (&#92;overline{f}g), &#92;lambda &#92;rangle = - &#92;langle &#92;frac{&#92;partial &#92;overline{f}}{&#92;partial x_i} g, &#92;lambda &#92;rangle - &#92;langle &#92;overline{f} &#92;frac{&#92;partial g}{&#92;partial x_i}, &#92;lambda &#92;rangle ' title='&#92;displaystyle  &#92;langle g, (&#92;frac{&#92;partial &#92;lambda}{&#92;partial x_i}) f &#92;rangle = &#92;langle &#92;overline{f} g, &#92;frac{&#92;partial &#92;lambda}{&#92;partial x_i} &#92;rangle = - &#92;langle &#92;frac{&#92;partial}{&#92;partial x_i} (&#92;overline{f}g), &#92;lambda &#92;rangle = - &#92;langle &#92;frac{&#92;partial &#92;overline{f}}{&#92;partial x_i} g, &#92;lambda &#92;rangle - &#92;langle &#92;overline{f} &#92;frac{&#92;partial g}{&#92;partial x_i}, &#92;lambda &#92;rangle ' class='latex' /></p>
<p> And for the other summand we see
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Clangle+g%2C+%5Clambda+%28%5Cfrac%7B%5Cpartial+f%7D%7B%5Cpartial+x_i%7D%29+%5Crangle+%3D+%5Clangle+%5Coverline%7B%5Cfrac%7B%5Cpartial+f%7D%7B%5Cpartial+x_i%7D%7D+g%2C+%5Clambda+%5Crangle+%3D+%5Clangle+%5Cfrac%7B%5Cpartial+%5Coverline%7Bf%7D%7D%7B%5Cpartial+x_i%7D+g%2C+%5Clambda+%5Crangle+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;langle g, &#92;lambda (&#92;frac{&#92;partial f}{&#92;partial x_i}) &#92;rangle = &#92;langle &#92;overline{&#92;frac{&#92;partial f}{&#92;partial x_i}} g, &#92;lambda &#92;rangle = &#92;langle &#92;frac{&#92;partial &#92;overline{f}}{&#92;partial x_i} g, &#92;lambda &#92;rangle ' title='&#92;displaystyle  &#92;langle g, &#92;lambda (&#92;frac{&#92;partial f}{&#92;partial x_i}) &#92;rangle = &#92;langle &#92;overline{&#92;frac{&#92;partial f}{&#92;partial x_i}} g, &#92;lambda &#92;rangle = &#92;langle &#92;frac{&#92;partial &#92;overline{f}}{&#92;partial x_i} g, &#92;lambda &#92;rangle ' class='latex' /></p>
<p>
Adding the last two sums we obtain
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Cbegin%7Barray%7D%7Brcl%7D++%5Clangle+g%2C+%28%5Cfrac%7B%5Cpartial+%5Clambda%7D%7B%5Cpartial+x_i%7D%29+f+%2B+%5Clambda+%28%5Cfrac%7B%5Cpartial+f%7D%7B%5Cpartial+x_i%7D%29+%5Crangle+%3D+%26+%5Clangle+g%2C+%28%5Cfrac%7B%5Cpartial+%5Clambda%7D%7B%5Cpartial+x_i%7D%29+f+%5Crangle+%2B+%5Clangle+g%2C+%5Clambda+%28%5Cfrac%7B%5Cpartial+f%7D%7B%5Cpartial+x_i%7D%29+%5Crangle%5C+%3D+-+%5Clangle+%5Cfrac%7B%5Cpartial+%5Coverline%7Bf%7D%7D%7B%5Cpartial+x_i%7D+g%2C+%5Clambda+%5Crangle+-+%5Clangle+%5Coverline%7Bf%7D+%5Cfrac%7B%5Cpartial+g%7D%7B%5Cpartial+x_i%7D%2C+%5Clambda+%5Crangle+%2B+%5Clangle+%5Cfrac%7B%5Cpartial+%5Coverline%7Bf%7D%7D%7B%5Cpartial+x_i%7D+g%2C+%5Clambda+%5Crangle+%5C%5C+%26+%3D+-+%5Clangle+%5Coverline%7Bf%7D+%5Cfrac%7B%5Cpartial+g%7D%7B%5Cpartial+x_i%7D%2C+%5Clambda+%5Crangle+%3D+%5Clangle+g%2C+%5Cfrac%7B%5Cpartial%7D%7B%5Cpartial+x_i%7D+%28%5Clambda+f%29+%5Crangle+%5Cend%7Barray%7D+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;begin{array}{rcl}  &#92;langle g, (&#92;frac{&#92;partial &#92;lambda}{&#92;partial x_i}) f + &#92;lambda (&#92;frac{&#92;partial f}{&#92;partial x_i}) &#92;rangle = &amp; &#92;langle g, (&#92;frac{&#92;partial &#92;lambda}{&#92;partial x_i}) f &#92;rangle + &#92;langle g, &#92;lambda (&#92;frac{&#92;partial f}{&#92;partial x_i}) &#92;rangle&#92; = - &#92;langle &#92;frac{&#92;partial &#92;overline{f}}{&#92;partial x_i} g, &#92;lambda &#92;rangle - &#92;langle &#92;overline{f} &#92;frac{&#92;partial g}{&#92;partial x_i}, &#92;lambda &#92;rangle + &#92;langle &#92;frac{&#92;partial &#92;overline{f}}{&#92;partial x_i} g, &#92;lambda &#92;rangle &#92;&#92; &amp; = - &#92;langle &#92;overline{f} &#92;frac{&#92;partial g}{&#92;partial x_i}, &#92;lambda &#92;rangle = &#92;langle g, &#92;frac{&#92;partial}{&#92;partial x_i} (&#92;lambda f) &#92;rangle &#92;end{array} ' title='&#92;displaystyle  &#92;begin{array}{rcl}  &#92;langle g, (&#92;frac{&#92;partial &#92;lambda}{&#92;partial x_i}) f + &#92;lambda (&#92;frac{&#92;partial f}{&#92;partial x_i}) &#92;rangle = &amp; &#92;langle g, (&#92;frac{&#92;partial &#92;lambda}{&#92;partial x_i}) f &#92;rangle + &#92;langle g, &#92;lambda (&#92;frac{&#92;partial f}{&#92;partial x_i}) &#92;rangle&#92; = - &#92;langle &#92;frac{&#92;partial &#92;overline{f}}{&#92;partial x_i} g, &#92;lambda &#92;rangle - &#92;langle &#92;overline{f} &#92;frac{&#92;partial g}{&#92;partial x_i}, &#92;lambda &#92;rangle + &#92;langle &#92;frac{&#92;partial &#92;overline{f}}{&#92;partial x_i} g, &#92;lambda &#92;rangle &#92;&#92; &amp; = - &#92;langle &#92;overline{f} &#92;frac{&#92;partial g}{&#92;partial x_i}, &#92;lambda &#92;rangle = &#92;langle g, &#92;frac{&#92;partial}{&#92;partial x_i} (&#92;lambda f) &#92;rangle &#92;end{array} ' class='latex' /></p>
<p>
Since this equality holds for any test function <img src='http://s0.wp.com/latex.php?latex=%7Bg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g}' title='{g}' class='latex' /> we obtain our desired result
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Cfrac%7B%5Cpartial%7D%7B%5Cpartial+x_i%7D+%28%5Clambda+f%29+%3D+%5Cfrac%7B%5Cpartial+%5Clambda%7D%7B%5Cpartial+x_i%7D+f+%2B+%5Clambda+%5Cfrac%7B%5Cpartial+f%7D%7B%5Cpartial+x_i%7D+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;frac{&#92;partial}{&#92;partial x_i} (&#92;lambda f) = &#92;frac{&#92;partial &#92;lambda}{&#92;partial x_i} f + &#92;lambda &#92;frac{&#92;partial f}{&#92;partial x_i} ' title='&#92;displaystyle  &#92;frac{&#92;partial}{&#92;partial x_i} (&#92;lambda f) = &#92;frac{&#92;partial &#92;lambda}{&#92;partial x_i} f + &#92;lambda &#92;frac{&#92;partial f}{&#92;partial x_i} ' class='latex' /></p>
<p> Since we didn&#8217;t use any property special to the <img src='http://s0.wp.com/latex.php?latex=%7Bi%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i}' title='{i}' class='latex' />-th variable, the above equality holds for each <img src='http://s0.wp.com/latex.php?latex=%7Bi+%3D1%2C2%2C%5Cldots%2C+d%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i =1,2,&#92;ldots, d}' title='{i =1,2,&#92;ldots, d}' class='latex' />.</p>
<p>
<p><b> Exercise 22 </b></p>
<p> i.Just do the calculations. For any test function <img src='http://s0.wp.com/latex.php?latex=%7Bg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g}' title='{g}' class='latex' />,
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Cbegin%7Barray%7D%7Brcl%7D++%5Clangle+g%2C+%5Cdelta%5E%5Cprime+x+%5Crangle+%26+%3D+%5Clangle+%5Coverline%7Bx%7D+g%2C+%5Cdelta%5E%5Cprime+%5Crangle+%3D+%5Clangle+x+g%2C+%5Cdelta%5E%5Cprime+%5Crangle+%3D+-+%5Clangle+%5Cfrac%7Bd%7D%7Bdx%7D%28x+g%29%2C+%5Cdelta+%5Crangle+%3D+-+%5Clangle+g%2B+x+g%5E%5Cprime%2C+%5Cdelta+%5Crangle+%5C%5C+%26+%3D+-+%28g%280%29%2B0g%5E%5Cprime%280%29%29%3D-g%280%29%3D+-+%5Clangle+g%2C+%5Cdelta+%5Crangle+%3D+%5Clangle+g%2C+-%5Cdelta+%5Crangle+%5Cend%7Barray%7D+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;begin{array}{rcl}  &#92;langle g, &#92;delta^&#92;prime x &#92;rangle &amp; = &#92;langle &#92;overline{x} g, &#92;delta^&#92;prime &#92;rangle = &#92;langle x g, &#92;delta^&#92;prime &#92;rangle = - &#92;langle &#92;frac{d}{dx}(x g), &#92;delta &#92;rangle = - &#92;langle g+ x g^&#92;prime, &#92;delta &#92;rangle &#92;&#92; &amp; = - (g(0)+0g^&#92;prime(0))=-g(0)= - &#92;langle g, &#92;delta &#92;rangle = &#92;langle g, -&#92;delta &#92;rangle &#92;end{array} ' title='&#92;displaystyle  &#92;begin{array}{rcl}  &#92;langle g, &#92;delta^&#92;prime x &#92;rangle &amp; = &#92;langle &#92;overline{x} g, &#92;delta^&#92;prime &#92;rangle = &#92;langle x g, &#92;delta^&#92;prime &#92;rangle = - &#92;langle &#92;frac{d}{dx}(x g), &#92;delta &#92;rangle = - &#92;langle g+ x g^&#92;prime, &#92;delta &#92;rangle &#92;&#92; &amp; = - (g(0)+0g^&#92;prime(0))=-g(0)= - &#92;langle g, &#92;delta &#92;rangle = &#92;langle g, -&#92;delta &#92;rangle &#92;end{array} ' class='latex' /></p>
<p> Thus <img src='http://s0.wp.com/latex.php?latex=%7B%5Cdelta%5E%5Cprime+x+%3D+-+%5Cdelta%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;delta^&#92;prime x = - &#92;delta}' title='{&#92;delta^&#92;prime x = - &#92;delta}' class='latex' />.</p>
<p>
ii. From Exercise 16, <img src='http://s0.wp.com/latex.php?latex=%7B%5Cdelta+x+%3D0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;delta x =0}' title='{&#92;delta x =0}' class='latex' />, the derivative of 0 is 0, thus <img src='http://s0.wp.com/latex.php?latex=%7B0+%3D+%5Cfrac%7Bd%7D%7Bdx%7D%28%5Cdelta+x%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{0 = &#92;frac{d}{dx}(&#92;delta x)}' title='{0 = &#92;frac{d}{dx}(&#92;delta x)}' class='latex' />. We can then apply the chain rule from the previous exercise, and see that <img src='http://s0.wp.com/latex.php?latex=%7B0+%3D+%5Cdelta%5E%5Cprime+x+%2B+%5Cdelta%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{0 = &#92;delta^&#92;prime x + &#92;delta}' title='{0 = &#92;delta^&#92;prime x + &#92;delta}' class='latex' />. Therefore, <img src='http://s0.wp.com/latex.php?latex=%7B%5Cdelta%5E%5Cprime+x+%3D+-+%5Cdelta%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;delta^&#92;prime x = - &#92;delta}' title='{&#92;delta^&#92;prime x = - &#92;delta}' class='latex' />.</p>
<p>
iii. Let <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7B%5Cphi_n%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{&#92;phi_n&#92;}}' title='{&#92;{&#92;phi_n&#92;}}' class='latex' /> be a sequence of approximations to the identity. We want to show for any test function <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' />, that <img src='http://s0.wp.com/latex.php?latex=%7B%5Clim_%7Bn%5Crightarrow%5Cinfty%7D+%5Cint+f+%5Cphi_n%5E%5Cprime+dx+%3D+-f%5E%5Cprime%280%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;lim_{n&#92;rightarrow&#92;infty} &#92;int f &#92;phi_n^&#92;prime dx = -f^&#92;prime(0)}' title='{&#92;lim_{n&#92;rightarrow&#92;infty} &#92;int f &#92;phi_n^&#92;prime dx = -f^&#92;prime(0)}' class='latex' />. Well, <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' /> and each <img src='http://s0.wp.com/latex.php?latex=%7B%5Cphi_n%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;phi_n}' title='{&#92;phi_n}' class='latex' /> are smooth functions and therefore integration by parts is fair game, and we see that for each <img src='http://s0.wp.com/latex.php?latex=%7Bn%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{n}' title='{n}' class='latex' />, <img src='http://s0.wp.com/latex.php?latex=%7B%5Cint+f+%5Cphi_n%5E%5Cprime+dx+%3D+-+%5Cint+f%5E%5Cprime+%5Cphi_n+%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;int f &#92;phi_n^&#92;prime dx = - &#92;int f^&#92;prime &#92;phi_n }' title='{&#92;int f &#92;phi_n^&#92;prime dx = - &#92;int f^&#92;prime &#92;phi_n }' class='latex' />. Now <img src='http://s0.wp.com/latex.php?latex=%7Bf%5E%5Cprime%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f^&#92;prime}' title='{f^&#92;prime}' class='latex' /> is a also a test function, and by Exercise 10, <img src='http://s0.wp.com/latex.php?latex=%7B%5Clim_%7Bn%5Crightarrow%5Cinfty%7D+%5Cint+f%5E%5Cprime+%5Cphi_n+dx+%3D+f%5E%5Cprime%280%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;lim_{n&#92;rightarrow&#92;infty} &#92;int f^&#92;prime &#92;phi_n dx = f^&#92;prime(0)}' title='{&#92;lim_{n&#92;rightarrow&#92;infty} &#92;int f^&#92;prime &#92;phi_n dx = f^&#92;prime(0)}' class='latex' />. Therefore <img src='http://s0.wp.com/latex.php?latex=%7B%5Clim_%7Bn+%5Crightarrow%5Cinfty%7D+%5Cint+f+%5Cphi_n%5E%5Cprime+dx+%3D+-+f%5E%5Cprime%280%29+%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;lim_{n &#92;rightarrow&#92;infty} &#92;int f &#92;phi_n^&#92;prime dx = - f^&#92;prime(0) }' title='{&#92;lim_{n &#92;rightarrow&#92;infty} &#92;int f &#92;phi_n^&#92;prime dx = - f^&#92;prime(0) }' class='latex' />.</p>
<p>
By Exercise 10, the sequence <img src='http://s0.wp.com/latex.php?latex=%7B%5Cphi_n%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;phi_n}' title='{&#92;phi_n}' class='latex' /> converges in the sense of distributions to <img src='http://s0.wp.com/latex.php?latex=%7B%5Cdelta%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;delta}' title='{&#92;delta}' class='latex' />, and as we&#8217;ve just shown, the sequence <img src='http://s0.wp.com/latex.php?latex=%7B%5Cphi_n%5E%5Cprime%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;phi_n^&#92;prime}' title='{&#92;phi_n^&#92;prime}' class='latex' /> converges in the sense of distributions to <img src='http://s0.wp.com/latex.php?latex=%7B%5Cdelta%5E%5Cprime%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;delta^&#92;prime}' title='{&#92;delta^&#92;prime}' class='latex' />. Now differentiation is a continuous operation on the space of distribution. Thus, <img src='http://s0.wp.com/latex.php?latex=%7B%5Cdelta%5E%5Cprime%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;delta^&#92;prime}' title='{&#92;delta^&#92;prime}' class='latex' /> is the derivative of of <img src='http://s0.wp.com/latex.php?latex=%7B%5Cdelta%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;delta}' title='{&#92;delta}' class='latex' />.</p>
<p>
<p><b> Exercise 23 </b></p>
<p> i. Given any test function <img src='http://s0.wp.com/latex.php?latex=%7Bg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g}' title='{g}' class='latex' />, consider the following calculation, which makes use that the fundamental Theorem of Calculus applies to <img src='http://s0.wp.com/latex.php?latex=%7Bg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g}' title='{g}' class='latex' />, since <img src='http://s0.wp.com/latex.php?latex=%7Bg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g}' title='{g}' class='latex' /> is differentiable in the classical sense. The calculation makes use that <img src='http://s0.wp.com/latex.php?latex=%7Bg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g}' title='{g}' class='latex' /> is compactly supported, and thus is 0 for all sufficiently large values.
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Cbegin%7Barray%7D%7Brcl%7D++%5Clangle+g%2C+%5Cfrac%7Bd%7D%7Bdx%7D+1_%7B%5B0%2C%5Cinfty%29%7D+%5Crangle+%26+%3D+-+%5Clangle+g%5E%5Cprime%2C+1_%7B%5B0%2C%5Cinfty%29%7D+%5Crangle+%3D+-+%5Cint+g%5E%5Cprime+%5Coverline%7B1%7D_%7B%5B0%2C%5Cinfty%29%7D+%3D+-+%5Cint_0%5E%5Cinfty+g%5E%5Cprime%28x%29+dx+%3D+-+%5Clim_%7BM+%5Crightarrow+%5Cinfty%7D+%5Cint_0%5EM+g%5E%5Cprime%28x%29+dx+%5C%5C+%26+%3D+-+%5Clim_%7BM+%5Crightarrow+%5Cinfty%7D+%28g%28M%29-g%280%29%29+%3D+-+%280-g%280%29%29+%3D+g%280%29+%3D+%5Clangle+g%2C+%5Cdelta+%5Crangle+%5Cend%7Barray%7D+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;begin{array}{rcl}  &#92;langle g, &#92;frac{d}{dx} 1_{[0,&#92;infty)} &#92;rangle &amp; = - &#92;langle g^&#92;prime, 1_{[0,&#92;infty)} &#92;rangle = - &#92;int g^&#92;prime &#92;overline{1}_{[0,&#92;infty)} = - &#92;int_0^&#92;infty g^&#92;prime(x) dx = - &#92;lim_{M &#92;rightarrow &#92;infty} &#92;int_0^M g^&#92;prime(x) dx &#92;&#92; &amp; = - &#92;lim_{M &#92;rightarrow &#92;infty} (g(M)-g(0)) = - (0-g(0)) = g(0) = &#92;langle g, &#92;delta &#92;rangle &#92;end{array} ' title='&#92;displaystyle  &#92;begin{array}{rcl}  &#92;langle g, &#92;frac{d}{dx} 1_{[0,&#92;infty)} &#92;rangle &amp; = - &#92;langle g^&#92;prime, 1_{[0,&#92;infty)} &#92;rangle = - &#92;int g^&#92;prime &#92;overline{1}_{[0,&#92;infty)} = - &#92;int_0^&#92;infty g^&#92;prime(x) dx = - &#92;lim_{M &#92;rightarrow &#92;infty} &#92;int_0^M g^&#92;prime(x) dx &#92;&#92; &amp; = - &#92;lim_{M &#92;rightarrow &#92;infty} (g(M)-g(0)) = - (0-g(0)) = g(0) = &#92;langle g, &#92;delta &#92;rangle &#92;end{array} ' class='latex' /></p>
<p> Since this holds for all test functions, the derivative of <img src='http://s0.wp.com/latex.php?latex=%7B1_%7B%5B0%2C%5Cinfty%29%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{1_{[0,&#92;infty)}}' title='{1_{[0,&#92;infty)}}' class='latex' /> is <img src='http://s0.wp.com/latex.php?latex=%7B%5Cdelta%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;delta}' title='{&#92;delta}' class='latex' />.</p>
<p>
ii. Again, given any test function <img src='http://s0.wp.com/latex.php?latex=%7Bg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g}' title='{g}' class='latex' />, and utilizing the same properties of <img src='http://s0.wp.com/latex.php?latex=%7Bg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g}' title='{g}' class='latex' /> as before.
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Cbegin%7Barray%7D%7Brcl%7D++%5Clangle+g%2C+%5Cfrac%7Bd%7D%7Bdx%7D+sgn+%5Crangle+%26+%3D+-+%5Clangle+g%5E%5Cprime%2C+sgn+%5Crangle+%3D+-+%5Cint_%7B-%5Cinfty%7D%5E%5Cinfty+g%5E%5Cprime%28x%29+%5Coverline%7Bsgn%7D+%28x%29+dx+%3D+-+%5Cint_%7B-%5Cinfty%7D%5E%5Cinfty+g%5E%5Cprime%28x%29+sgn+%28x%29+dx+%5C%5C+%26%3D+-+%5Cint_0%5E%5Cinfty+g%5E%5Cprime%28x%29+dx+%2B+%5Cint_%7B-%5Cinfty%7D%5E0+g%5E%5Cprime%28x%29+dx+%3D+-%280-g%280%29%29%2B%28g%280%29-0%29+%5C%5C+%26+%3D2+g%280%29+%3D+%5Clangle+g%2C+2%5Cdelta+%5Crangle+%5Cend%7Barray%7D+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;begin{array}{rcl}  &#92;langle g, &#92;frac{d}{dx} sgn &#92;rangle &amp; = - &#92;langle g^&#92;prime, sgn &#92;rangle = - &#92;int_{-&#92;infty}^&#92;infty g^&#92;prime(x) &#92;overline{sgn} (x) dx = - &#92;int_{-&#92;infty}^&#92;infty g^&#92;prime(x) sgn (x) dx &#92;&#92; &amp;= - &#92;int_0^&#92;infty g^&#92;prime(x) dx + &#92;int_{-&#92;infty}^0 g^&#92;prime(x) dx = -(0-g(0))+(g(0)-0) &#92;&#92; &amp; =2 g(0) = &#92;langle g, 2&#92;delta &#92;rangle &#92;end{array} ' title='&#92;displaystyle  &#92;begin{array}{rcl}  &#92;langle g, &#92;frac{d}{dx} sgn &#92;rangle &amp; = - &#92;langle g^&#92;prime, sgn &#92;rangle = - &#92;int_{-&#92;infty}^&#92;infty g^&#92;prime(x) &#92;overline{sgn} (x) dx = - &#92;int_{-&#92;infty}^&#92;infty g^&#92;prime(x) sgn (x) dx &#92;&#92; &amp;= - &#92;int_0^&#92;infty g^&#92;prime(x) dx + &#92;int_{-&#92;infty}^0 g^&#92;prime(x) dx = -(0-g(0))+(g(0)-0) &#92;&#92; &amp; =2 g(0) = &#92;langle g, 2&#92;delta &#92;rangle &#92;end{array} ' class='latex' /></p>
<p> Since this holds for any test function, the derivative of <img src='http://s0.wp.com/latex.php?latex=%7Bsgn%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{sgn}' title='{sgn}' class='latex' /> is <img src='http://s0.wp.com/latex.php?latex=%7B2+%5Cdelta%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{2 &#92;delta}' title='{2 &#92;delta}' class='latex' />.</p>
<p>
iii.</p>
<p>
iv.</p>
<p>
v. For the last, time chose an test function <img src='http://s0.wp.com/latex.php?latex=%7Bg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g}' title='{g}' class='latex' />, then
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Cbegin%7Barray%7D%7Brcl%7D++%5Clangle+g%2C+%5Cfrac%7Bd%7D%7Bdx%7D%28%7Cx%7C%29+%5Crangle+%26+%3D+-+%5Clangle+g%5E%5Cprime%2C+%7Cx%7C+%5Crangle+%3D+-+%5Cint+g%5E%5Cprime%28x%29%5Coverline%7B%7Cx%7C%7D+dx+%5C%5C+%26+%3D+-%5Cint_0%5E%5Cinfty+g%5E%5Cprime%28x%29+x+dx+%2B+%5Cint_%7B-%5Cinfty%7D%5E0+g%5E%5Cprime+%28x%29+x+dx+%5Cend%7Barray%7D+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;begin{array}{rcl}  &#92;langle g, &#92;frac{d}{dx}(|x|) &#92;rangle &amp; = - &#92;langle g^&#92;prime, |x| &#92;rangle = - &#92;int g^&#92;prime(x)&#92;overline{|x|} dx &#92;&#92; &amp; = -&#92;int_0^&#92;infty g^&#92;prime(x) x dx + &#92;int_{-&#92;infty}^0 g^&#92;prime (x) x dx &#92;end{array} ' title='&#92;displaystyle  &#92;begin{array}{rcl}  &#92;langle g, &#92;frac{d}{dx}(|x|) &#92;rangle &amp; = - &#92;langle g^&#92;prime, |x| &#92;rangle = - &#92;int g^&#92;prime(x)&#92;overline{|x|} dx &#92;&#92; &amp; = -&#92;int_0^&#92;infty g^&#92;prime(x) x dx + &#92;int_{-&#92;infty}^0 g^&#92;prime (x) x dx &#92;end{array} ' class='latex' /></p>
<p>
Now both <img src='http://s0.wp.com/latex.php?latex=%7Bg%5E%5Cprime%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g^&#92;prime}' title='{g^&#92;prime}' class='latex' /> and <img src='http://s0.wp.com/latex.php?latex=%7Bx%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x}' title='{x}' class='latex' /> are differentiable, so integration by parts shows us
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Cint_a%5Eb+g%5E%5Cprime%28x%29+x+dx+%3D+g%28b%29b-g%28a%29a+-+%5Cint_a%5Eb+g%28x%29dx+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;int_a^b g^&#92;prime(x) x dx = g(b)b-g(a)a - &#92;int_a^b g(x)dx ' title='&#92;displaystyle  &#92;int_a^b g^&#92;prime(x) x dx = g(b)b-g(a)a - &#92;int_a^b g(x)dx ' class='latex' /></p>
<p>n The other thing we should note is that <img src='http://s0.wp.com/latex.php?latex=%7Bx+g%28x%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x g(x)}' title='{x g(x)}' class='latex' /> has compact support and thus vanishes outside a bounded area. Therefore
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Cbegin%7Barray%7D%7Brcl%7D++%5Clangle+g%2C+%5Cfrac%7Bd%7D%7Bdx%7D+%28%7Cx%7C%29+%5Crangle+%26+%3D+-%5Cint_0%5E%5Cinfty+g%5E%5Cprime%28x%29+x+dx+%2B+%5Cint_%7B-%5Cinfty%7D%5E0+g%5E%5Cprime+%28x%29+x+dx+%5C%5C+%26+%3D+-%5Cleft%280-g%280%29%280%29+-+%5Cint_0%5E%5Cinfty+g%28x%29dx+%5Cright%29+%2B+%5Cleft%28g%280%290-0+-+%5Cint_%7B-%5Cinfty%7D%5E0+g%28x%29dx+%5Cright%29+%5C%5C+%26+%3D+%5Cint_0%5E%5Cinfty+g%28x%29dx+-+%5Cint_%7B-%5Cinfty%7D%5E0+g%28x%29dx+%3D+%5Cint+g%28x%29+sgn+%28x%29+dx+%5C%5C+%26+%3D+%5Clangle+g%2C+sgn+%5Crangle+%5Cend%7Barray%7D+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;begin{array}{rcl}  &#92;langle g, &#92;frac{d}{dx} (|x|) &#92;rangle &amp; = -&#92;int_0^&#92;infty g^&#92;prime(x) x dx + &#92;int_{-&#92;infty}^0 g^&#92;prime (x) x dx &#92;&#92; &amp; = -&#92;left(0-g(0)(0) - &#92;int_0^&#92;infty g(x)dx &#92;right) + &#92;left(g(0)0-0 - &#92;int_{-&#92;infty}^0 g(x)dx &#92;right) &#92;&#92; &amp; = &#92;int_0^&#92;infty g(x)dx - &#92;int_{-&#92;infty}^0 g(x)dx = &#92;int g(x) sgn (x) dx &#92;&#92; &amp; = &#92;langle g, sgn &#92;rangle &#92;end{array} ' title='&#92;displaystyle  &#92;begin{array}{rcl}  &#92;langle g, &#92;frac{d}{dx} (|x|) &#92;rangle &amp; = -&#92;int_0^&#92;infty g^&#92;prime(x) x dx + &#92;int_{-&#92;infty}^0 g^&#92;prime (x) x dx &#92;&#92; &amp; = -&#92;left(0-g(0)(0) - &#92;int_0^&#92;infty g(x)dx &#92;right) + &#92;left(g(0)0-0 - &#92;int_{-&#92;infty}^0 g(x)dx &#92;right) &#92;&#92; &amp; = &#92;int_0^&#92;infty g(x)dx - &#92;int_{-&#92;infty}^0 g(x)dx = &#92;int g(x) sgn (x) dx &#92;&#92; &amp; = &#92;langle g, sgn &#92;rangle &#92;end{array} ' class='latex' /></p>
<p> The derivative of <img src='http://s0.wp.com/latex.php?latex=%7B%7Cx%7C%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{|x|}' title='{|x|}' class='latex' /> as distribution is <img src='http://s0.wp.com/latex.php?latex=%7Bsgn%28x%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{sgn(x)}' title='{sgn(x)}' class='latex' />.</p>
<p>
<p><b> Exercise 24 </b></p>
<p> Choose any distribution <img src='http://s0.wp.com/latex.php?latex=%7B%5Clambda%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;lambda}' title='{&#92;lambda}' class='latex' />, and any test function <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' />. We immediately see that for any <img src='http://s0.wp.com/latex.php?latex=%7B1%5Cleq+i%2Cj+%5Cleq+d%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{1&#92;leq i,j &#92;leq d}' title='{1&#92;leq i,j &#92;leq d}' class='latex' />
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Clangle+f%2C+%5Cfrac%7B%5Cpartial%7D%7B%5Cpartial+x_i%7D%5Cfrac%7B%5Cpartial%7D%7B%5Cpartial+x_j%7D+%5Clambda+%5Crangle+%3D+%5Clangle+%5Cfrac%7B%5Cpartial%7D%7B%5Cpartial+x_j%7D%5Cfrac%7B%5Cpartial%7D%7B%5Cpartial+x_i%7D+f%2C+%5Clambda+%5Crangle+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;langle f, &#92;frac{&#92;partial}{&#92;partial x_i}&#92;frac{&#92;partial}{&#92;partial x_j} &#92;lambda &#92;rangle = &#92;langle &#92;frac{&#92;partial}{&#92;partial x_j}&#92;frac{&#92;partial}{&#92;partial x_i} f, &#92;lambda &#92;rangle ' title='&#92;displaystyle  &#92;langle f, &#92;frac{&#92;partial}{&#92;partial x_i}&#92;frac{&#92;partial}{&#92;partial x_j} &#92;lambda &#92;rangle = &#92;langle &#92;frac{&#92;partial}{&#92;partial x_j}&#92;frac{&#92;partial}{&#92;partial x_i} f, &#92;lambda &#92;rangle ' class='latex' /></p>
<p> and similarly
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Clangle+f%2C+%5Cfrac%7B%5Cpartial%7D%7B%5Cpartial+x_j%7D%5Cfrac%7B%5Cpartial%7D%7B%5Cpartial+x_i%7D+%5Clambda+%5Crangle+%3D+%5Clangle+%5Cfrac%7B%5Cpartial%7D%7B%5Cpartial+x_i%7D%5Cfrac%7B%5Cpartial%7D%7B%5Cpartial+x_j%7D+f%2C+%5Clambda+%5Crangle+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;langle f, &#92;frac{&#92;partial}{&#92;partial x_j}&#92;frac{&#92;partial}{&#92;partial x_i} &#92;lambda &#92;rangle = &#92;langle &#92;frac{&#92;partial}{&#92;partial x_i}&#92;frac{&#92;partial}{&#92;partial x_j} f, &#92;lambda &#92;rangle ' title='&#92;displaystyle  &#92;langle f, &#92;frac{&#92;partial}{&#92;partial x_j}&#92;frac{&#92;partial}{&#92;partial x_i} &#92;lambda &#92;rangle = &#92;langle &#92;frac{&#92;partial}{&#92;partial x_i}&#92;frac{&#92;partial}{&#92;partial x_j} f, &#92;lambda &#92;rangle ' class='latex' /></p>
<p> <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' /> is smooth, and therefore <img src='http://s0.wp.com/latex.php?latex=%7B%5Cfrac%7B%5Cpartial%5E2+f%7D%7B%5Cpartial+x_i+%5Cpartial+x_j%7D+%3D%5Cfrac%7B%5Cpartial%5E2+f%7D%7B%5Cpartial+x_j+%5Cpartial+x_i%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;frac{&#92;partial^2 f}{&#92;partial x_i &#92;partial x_j} =&#92;frac{&#92;partial^2 f}{&#92;partial x_j &#92;partial x_i}}' title='{&#92;frac{&#92;partial^2 f}{&#92;partial x_i &#92;partial x_j} =&#92;frac{&#92;partial^2 f}{&#92;partial x_j &#92;partial x_i}}' class='latex' />. Thus we see
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Clangle+f%2C+%5Cfrac%7B%5Cpartial%7D%7B%5Cpartial+x_i%7D%5Cfrac%7B%5Cpartial%7D%7B%5Cpartial+x_j%7D+%5Clambda+%5Crangle+%3D+%5Clangle+f%2C+%5Cfrac%7B%5Cpartial%7D%7B%5Cpartial+x_j%7D%5Cfrac%7B%5Cpartial%7D%7B%5Cpartial+x_i%7D+%5Clambda+%5Crangle+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;langle f, &#92;frac{&#92;partial}{&#92;partial x_i}&#92;frac{&#92;partial}{&#92;partial x_j} &#92;lambda &#92;rangle = &#92;langle f, &#92;frac{&#92;partial}{&#92;partial x_j}&#92;frac{&#92;partial}{&#92;partial x_i} &#92;lambda &#92;rangle ' title='&#92;displaystyle  &#92;langle f, &#92;frac{&#92;partial}{&#92;partial x_i}&#92;frac{&#92;partial}{&#92;partial x_j} &#92;lambda &#92;rangle = &#92;langle f, &#92;frac{&#92;partial}{&#92;partial x_j}&#92;frac{&#92;partial}{&#92;partial x_i} &#92;lambda &#92;rangle ' class='latex' /></p>
<p> for each test function <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' />.</p>
<p>
We therefore have <img src='http://s0.wp.com/latex.php?latex=%7B%5Cfrac%7B%5Cpartial%7D%7B%5Cpartial+x_i%7D%5Cfrac%7B%5Cpartial%7D%7B%5Cpartial+x_j%7D+%5Clambda+%3D+%5Cfrac%7B%5Cpartial%7D%7B%5Cpartial+x_j%7D%5Cfrac%7B%5Cpartial%7D%7B%5Cpartial+x_i%7D+%5Clambda%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;frac{&#92;partial}{&#92;partial x_i}&#92;frac{&#92;partial}{&#92;partial x_j} &#92;lambda = &#92;frac{&#92;partial}{&#92;partial x_j}&#92;frac{&#92;partial}{&#92;partial x_i} &#92;lambda}' title='{&#92;frac{&#92;partial}{&#92;partial x_i}&#92;frac{&#92;partial}{&#92;partial x_j} &#92;lambda = &#92;frac{&#92;partial}{&#92;partial x_j}&#92;frac{&#92;partial}{&#92;partial x_i} &#92;lambda}' class='latex' />. Weak derivatives commute.</p>
<p>
<p><b> Exercise 29 </b></p>
<p> We need to show that if <img src='http://s0.wp.com/latex.php?latex=%7Bf_n+%5Crightarrow+f%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f_n &#92;rightarrow f}' title='{f_n &#92;rightarrow f}' class='latex' /> in <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmathcal%7BS%7D%28%7B%5Cmathbb+R%7D%5Ed%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mathcal{S}({&#92;mathbb R}^d)}' title='{&#92;mathcal{S}({&#92;mathbb R}^d)}' class='latex' />, then <img src='http://s0.wp.com/latex.php?latex=%7B%5Clangle+f_n%2C+%5Cmu+%5Crangle+%5Crightarrow+%5Clangle+f%2C+%5Cmu+%5Crangle%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;langle f_n, &#92;mu &#92;rangle &#92;rightarrow &#92;langle f, &#92;mu &#92;rangle}' title='{&#92;langle f_n, &#92;mu &#92;rangle &#92;rightarrow &#92;langle f, &#92;mu &#92;rangle}' class='latex' />. Actually, we&#8217;ll simplify our lives by showing that each element in the Schwartz class is absolutely integrable with respect to the measure <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmu%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mu}' title='{&#92;mu}' class='latex' />. By doing that, then <img src='http://s0.wp.com/latex.php?latex=%7Bg+%5Crightarrow+%5Clangle+g%2C+%5Cmu+%5Crangle+%3D+%5Cint_%7B%7B%5Cmathbb+R%7D%5Ed%7D+g+d%5Coverline%7B%5Cmu%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g &#92;rightarrow &#92;langle g, &#92;mu &#92;rangle = &#92;int_{{&#92;mathbb R}^d} g d&#92;overline{&#92;mu}}' title='{g &#92;rightarrow &#92;langle g, &#92;mu &#92;rangle = &#92;int_{{&#92;mathbb R}^d} g d&#92;overline{&#92;mu}}' class='latex' /> is automatically a linear map from <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmathcal%7BS%7D%28%7B%5Cmathbb+R%7D%5Ed%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mathcal{S}({&#92;mathbb R}^d)}' title='{&#92;mathcal{S}({&#92;mathbb R}^d)}' class='latex' /> to <img src='http://s0.wp.com/latex.php?latex=%7B%7B%5Cmathbb+C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{{&#92;mathbb C}}' title='{{&#92;mathbb C}}' class='latex' />. If we show that, then we can assume without less of generality, that our sequence <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7Bf_n%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{f_n&#92;}}' title='{&#92;{f_n&#92;}}' class='latex' /> converges to 0.</p>
<p>
Let <img src='http://s0.wp.com/latex.php?latex=%7Bg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g}' title='{g}' class='latex' /> lie in the Schwartz class. Let <img src='http://s0.wp.com/latex.php?latex=%7BC_n+%3D+%5C%7Bx+%5Cin+%7B%5Cmathbb+R%7D%5Ed+%3A+n+%3C+x+%5Cleq+n%2B1%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C_n = &#92;{x &#92;in {&#92;mathbb R}^d : n &lt; x &#92;leq n+1&#92;}}' title='{C_n = &#92;{x &#92;in {&#92;mathbb R}^d : n &lt; x &#92;leq n+1&#92;}}' class='latex' />. Then <img src='http://s0.wp.com/latex.php?latex=%7B%5Cint+%7Cg%7C+d%7C%5Cmu%7C+%3D+%5Cint_%7B%7Cx%7C+%5Cleq+1%7D%7Cg%7C+d%7C%5Cmu%7C+%2B+%5Csum_%7BN%3D1%7D%5E%5Cinfty+%5Cint_%7BC_n%7D+%7Cg%7C+d%7C%5Cmu%7C%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;int |g| d|&#92;mu| = &#92;int_{|x| &#92;leq 1}|g| d|&#92;mu| + &#92;sum_{N=1}^&#92;infty &#92;int_{C_n} |g| d|&#92;mu|}' title='{&#92;int |g| d|&#92;mu| = &#92;int_{|x| &#92;leq 1}|g| d|&#92;mu| + &#92;sum_{N=1}^&#92;infty &#92;int_{C_n} |g| d|&#92;mu|}' class='latex' />. Now <img src='http://s0.wp.com/latex.php?latex=%7Bg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g}' title='{g}' class='latex' /> is rapidly decreasing, since it&#039;s Schwartz. So <img src='http://s0.wp.com/latex.php?latex=%7B%5Csup_%7Bx%7D+%7Cx%7C%5E%7Bk%2B2%7D%7Cg%28x%29%7C+%3C+%5Cinfty%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;sup_{x} |x|^{k+2}|g(x)| &lt; &#92;infty}' title='{&#92;sup_{x} |x|^{k+2}|g(x)| &lt; &#92;infty}' class='latex' />, thus <img src='http://s0.wp.com/latex.php?latex=%7B%7Cg%28x%29%7C++0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{|g(x)|  0}' title='{|g(x)|  0}' class='latex' />, for all <img src='http://s0.wp.com/latex.php?latex=%7Bx+%5Cneq+0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x &#92;neq 0}' title='{x &#92;neq 0}' class='latex' />.</p>
<p>
Therefore, given any <img src='http://s0.wp.com/latex.php?latex=%7Bn+%5Cgeq+1%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{n &#92;geq 1}' title='{n &#92;geq 1}' class='latex' />.
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Cbegin%7Barray%7D%7Brcl%7D++%5Cint_%7BC_n%7D+%7Cg%7C+d%7C%5Cmu%7C+%26+%5Cleq+%5Cint_%7BC_n%7D+%5Cfrac%7BB%7D%7B%7Cx%7C%5E%7Bk%2B2%7D%7D+d%7C%5Cmu%7C+%5Cleq+%5Cleft%28%5Csup_%7Bx+%5Cin+C_n%7D+%5Cfrac%7BB%7D%7B%7Cx%7C%5E%7Bk%2B2%7D%7D+%5Cright%29+%7C%5Cmu%7C%5Cleft%28C_n%5Cright%29+%5C%5C+%26+%5Cleq+%5Cfrac%7BB%7D%7Bn%5E%7Bk%2B2%7D%7D+%7C%5Cmu%7C%5Cleft%28B%280%2Cn%2B1%29%5Cright%29+%5Cleq+%5Cfrac%7BB%7D%7Bn%5E%7Bk%2B2%7D%7D+C%28n%2B1%29%5Ek+%3D+%5Cfrac%7BBC%7D%7Bn%5E2%7D+%7B%5Cleft%281%2B%5Cfrac%7B1%7D%7Bn%7D%5Cright%29%7D%5Ek+%5C%5C+%26+%5Cleq+%5Cfrac%7BBC%7D%7Bn%5E2%7D+2%5Ek+%3D+%5Cfrac%7B2%5EkBC%7D%7Bn%5E2%7D+%5Cend%7Barray%7D+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;begin{array}{rcl}  &#92;int_{C_n} |g| d|&#92;mu| &amp; &#92;leq &#92;int_{C_n} &#92;frac{B}{|x|^{k+2}} d|&#92;mu| &#92;leq &#92;left(&#92;sup_{x &#92;in C_n} &#92;frac{B}{|x|^{k+2}} &#92;right) |&#92;mu|&#92;left(C_n&#92;right) &#92;&#92; &amp; &#92;leq &#92;frac{B}{n^{k+2}} |&#92;mu|&#92;left(B(0,n+1)&#92;right) &#92;leq &#92;frac{B}{n^{k+2}} C(n+1)^k = &#92;frac{BC}{n^2} {&#92;left(1+&#92;frac{1}{n}&#92;right)}^k &#92;&#92; &amp; &#92;leq &#92;frac{BC}{n^2} 2^k = &#92;frac{2^kBC}{n^2} &#92;end{array} ' title='&#92;displaystyle  &#92;begin{array}{rcl}  &#92;int_{C_n} |g| d|&#92;mu| &amp; &#92;leq &#92;int_{C_n} &#92;frac{B}{|x|^{k+2}} d|&#92;mu| &#92;leq &#92;left(&#92;sup_{x &#92;in C_n} &#92;frac{B}{|x|^{k+2}} &#92;right) |&#92;mu|&#92;left(C_n&#92;right) &#92;&#92; &amp; &#92;leq &#92;frac{B}{n^{k+2}} |&#92;mu|&#92;left(B(0,n+1)&#92;right) &#92;leq &#92;frac{B}{n^{k+2}} C(n+1)^k = &#92;frac{BC}{n^2} {&#92;left(1+&#92;frac{1}{n}&#92;right)}^k &#92;&#92; &amp; &#92;leq &#92;frac{BC}{n^2} 2^k = &#92;frac{2^kBC}{n^2} &#92;end{array} ' class='latex' /></p>
<p> Thus the series <img src='http://s0.wp.com/latex.php?latex=%7B%5Csum_%7Bn%3D1%7D%5E%5Cinfty+%5Cint_%7BC_n%7D%7Cg%7Cd%7C%5Cmu%7C%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;sum_{n=1}^&#92;infty &#92;int_{C_n}|g|d|&#92;mu|}' title='{&#92;sum_{n=1}^&#92;infty &#92;int_{C_n}|g|d|&#92;mu|}' class='latex' /> is term-wise dominated by the series <img src='http://s0.wp.com/latex.php?latex=%7B2%5Ek+BC+%5Csum_%7Bn%3D1%7D%5E%5Cinfty+%5Cfrac%7B1%7D%7Bn%5E2%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{2^k BC &#92;sum_{n=1}^&#92;infty &#92;frac{1}{n^2}}' title='{2^k BC &#92;sum_{n=1}^&#92;infty &#92;frac{1}{n^2}}' class='latex' />, which converges. Since each term of the first series is non-negative, that must mean that the first series converges. And since <img src='http://s0.wp.com/latex.php?latex=%7B%5Cint_%7B%7Cx%7C%5Cleq+1%7D%7Cg%7Cd%7C%5Cmu%7C+%5Cleq+C%28+%5Csup_%7Bx+%5Cin+%7B%5Cmathbb+R%7D%5Ed%7D%7Cg%28x%29%7C%29%3C+%5Cinfty%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;int_{|x|&#92;leq 1}|g|d|&#92;mu| &#92;leq C( &#92;sup_{x &#92;in {&#92;mathbb R}^d}|g(x)|)&lt; &#92;infty}' title='{&#92;int_{|x|&#92;leq 1}|g|d|&#92;mu| &#92;leq C( &#92;sup_{x &#92;in {&#92;mathbb R}^d}|g(x)|)&lt; &#92;infty}' class='latex' />, we see that <img src='http://s0.wp.com/latex.php?latex=%7B%5Cint+%7Cg%7Cd%7C%5Cmu%7C+%3C+%5Cinfty%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;int |g|d|&#92;mu| &lt; &#92;infty}' title='{&#92;int |g|d|&#92;mu| &lt; &#92;infty}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7Bg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g}' title='{g}' class='latex' /> is absolutely integrable with respect to <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmu%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mu}' title='{&#92;mu}' class='latex' />. Since our pick of <img src='http://s0.wp.com/latex.php?latex=%7Bg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g}' title='{g}' class='latex' /> was arbitrary, each Schwartz function is absolutely integrable with respect to <img src='http://s0.wp.com/latex.php?latex=%7B%5Coverline%7B%5Cmu%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;overline{&#92;mu}}' title='{&#92;overline{&#92;mu}}' class='latex' />. For the reasons we stated before, the map <img src='http://s0.wp.com/latex.php?latex=%7Bg+%5Crightarrow+%5Clangle+g%2C+%5Cmu+%5Crangle+%3D+%5Cint+g+d%5Coverline%7B%5Cmu%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g &#92;rightarrow &#92;langle g, &#92;mu &#92;rangle = &#92;int g d&#92;overline{&#92;mu}}' title='{g &#92;rightarrow &#92;langle g, &#92;mu &#92;rangle = &#92;int g d&#92;overline{&#92;mu}}' class='latex' /> is linear.</p>
<p>
So assume that <img src='http://s0.wp.com/latex.php?latex=%7Bf_n+%5Crightarrow+0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f_n &#92;rightarrow 0}' title='{f_n &#92;rightarrow 0}' class='latex' /> in <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmathcal%7BS%7D%28%7B%5Cmathbb+R%7D%5Ed%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mathcal{S}({&#92;mathbb R}^d)}' title='{&#92;mathcal{S}({&#92;mathbb R}^d)}' class='latex' />. By definition, that means that for each non-negative integers <img src='http://s0.wp.com/latex.php?latex=%7Bi%2Cm%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i,m}' title='{i,m}' class='latex' />, we have <img src='http://s0.wp.com/latex.php?latex=%7B%5Csup_%7Bx+%5Cin+%7B%5Cmathbb+R%7D%5Ed%7D%7Cx%7C%5Ei+%7C%5Cnabla%5Ei+f_n%28x%29%7C+%5Crightarrow+0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;sup_{x &#92;in {&#92;mathbb R}^d}|x|^i |&#92;nabla^i f_n(x)| &#92;rightarrow 0}' title='{&#92;sup_{x &#92;in {&#92;mathbb R}^d}|x|^i |&#92;nabla^i f_n(x)| &#92;rightarrow 0}' class='latex' />. Thus, given any <img src='http://s0.wp.com/latex.php?latex=%7B%5Cdelta+%3E+0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;delta &gt; 0}' title='{&#92;delta &gt; 0}' class='latex' />, there exists an <img src='http://s0.wp.com/latex.php?latex=%7BN%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{N}' title='{N}' class='latex' /> such that if <img src='http://s0.wp.com/latex.php?latex=%7Bn+%3E+N%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{n &gt; N}' title='{n &gt; N}' class='latex' />, then <img src='http://s0.wp.com/latex.php?latex=%7B+%5Csup_%7Bx+%5Cin+%7B%5Cmathbb+R%7D%5Ed%7D+%7Cx%7C%5E%7Bk%2B2%7D+%7Cf_n%28x%29%7C++N%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{ &#92;sup_{x &#92;in {&#92;mathbb R}^d} |x|^{k+2} |f_n(x)|  N}' title='{ &#92;sup_{x &#92;in {&#92;mathbb R}^d} |x|^{k+2} |f_n(x)|  N}' class='latex' />,
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Cint_%7B%7Cx%7C%3E1%7Df_n+d%5Coverline%7B%5Cmu%7D+%5Cleq+%5Cint_%7B%7Cx%7C%3E1%7D%7Cf_n%7Cd%7C%5Cmu%7C+%3D+%5Csum_%7Bm%3D1%7D%5E%5Cinfty+%5Cint_%7BC_m%7D%7Cf_n%7Cd%7C%5Cmu%7C+%5Cleq+2%5Ek+C+%5Cepsilon+%5Csum_%7Bm%3D1%7D%5E%5Cinfty+%5Cfrac%7B1%7D%7Bm%5E2%7D+%3D+%5Cfrac%7B%5Cpi%5E2+2%5Ek+C%7D%7B6%7D+%5Cepsilon+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;int_{|x|&gt;1}f_n d&#92;overline{&#92;mu} &#92;leq &#92;int_{|x|&gt;1}|f_n|d|&#92;mu| = &#92;sum_{m=1}^&#92;infty &#92;int_{C_m}|f_n|d|&#92;mu| &#92;leq 2^k C &#92;epsilon &#92;sum_{m=1}^&#92;infty &#92;frac{1}{m^2} = &#92;frac{&#92;pi^2 2^k C}{6} &#92;epsilon ' title='&#92;displaystyle  &#92;int_{|x|&gt;1}f_n d&#92;overline{&#92;mu} &#92;leq &#92;int_{|x|&gt;1}|f_n|d|&#92;mu| = &#92;sum_{m=1}^&#92;infty &#92;int_{C_m}|f_n|d|&#92;mu| &#92;leq 2^k C &#92;epsilon &#92;sum_{m=1}^&#92;infty &#92;frac{1}{m^2} = &#92;frac{&#92;pi^2 2^k C}{6} &#92;epsilon ' class='latex' /></p>
<p> Since <img src='http://s0.wp.com/latex.php?latex=%7B%5Cfrac%7B%5Cpi%5E2+2%5Ek+C%7D%7B6%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;frac{&#92;pi^2 2^k C}{6}}' title='{&#92;frac{&#92;pi^2 2^k C}{6}}' class='latex' /> is just some constant that doesn&#8217;t depend on <img src='http://s0.wp.com/latex.php?latex=%7Bn%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{n}' title='{n}' class='latex' />, that means <img src='http://s0.wp.com/latex.php?latex=%7B+%5Clim_%7Bn+%5Crightarrow+%5Cinfty%7D+%5Cint+f_n+d%5Coverline%7B%5Cmu%7D+%3D0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{ &#92;lim_{n &#92;rightarrow &#92;infty} &#92;int f_n d&#92;overline{&#92;mu} =0}' title='{ &#92;lim_{n &#92;rightarrow &#92;infty} &#92;int f_n d&#92;overline{&#92;mu} =0}' class='latex' />.</p>
<p>
Similarly, <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7Cf_n%5C%7C%3D+%5Csup_%7Bx+%5Cin+%7B%5Cmathbb+R%7D%5Ed%7D+%7Cf%28x%29%7C%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;|f_n&#92;|= &#92;sup_{x &#92;in {&#92;mathbb R}^d} |f(x)|}' title='{&#92;|f_n&#92;|= &#92;sup_{x &#92;in {&#92;mathbb R}^d} |f(x)|}' class='latex' /> tends towards 0 as <img src='http://s0.wp.com/latex.php?latex=%7Bn%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{n}' title='{n}' class='latex' /> goes to <img src='http://s0.wp.com/latex.php?latex=%7B%5Cinfty%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;infty}' title='{&#92;infty}' class='latex' />. And since
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%7C%5Cint_%7B%7Cx%7C%5Cleq+1%7D+f_n+d%5Coverline%7B%5Cmu%7D+%7C+%5Cleq+%5Cint_%7B%7Cx%7C%5Cleq+1%7D+%7Cf_n%7C+d%7C%5Cmu%7C+%5Cleq+C%5C%7Cf_n%5C%7C+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  |&#92;int_{|x|&#92;leq 1} f_n d&#92;overline{&#92;mu} | &#92;leq &#92;int_{|x|&#92;leq 1} |f_n| d|&#92;mu| &#92;leq C&#92;|f_n&#92;| ' title='&#92;displaystyle  |&#92;int_{|x|&#92;leq 1} f_n d&#92;overline{&#92;mu} | &#92;leq &#92;int_{|x|&#92;leq 1} |f_n| d|&#92;mu| &#92;leq C&#92;|f_n&#92;| ' class='latex' /></p>
<p> we see that <img src='http://s0.wp.com/latex.php?latex=%7B%5Clim_%7Bn+%5Crightarrow+%5Cinfty%7D+%5Cint_%7B%7Cx%7C%5Cleq+1%7D+f_n+d%5Coverline%7B%5Cmu%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;lim_{n &#92;rightarrow &#92;infty} &#92;int_{|x|&#92;leq 1} f_n d&#92;overline{&#92;mu}}' title='{&#92;lim_{n &#92;rightarrow &#92;infty} &#92;int_{|x|&#92;leq 1} f_n d&#92;overline{&#92;mu}}' class='latex' /> is 0.</p>
<p>
Now since for each <img src='http://s0.wp.com/latex.php?latex=%7Bn%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{n}' title='{n}' class='latex' />, we can split <img src='http://s0.wp.com/latex.php?latex=%7B%5Cint+f_n+d%5Coverline%7B%5Cmu%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;int f_n d&#92;overline{&#92;mu}}' title='{&#92;int f_n d&#92;overline{&#92;mu}}' class='latex' /> into the sum <img src='http://s0.wp.com/latex.php?latex=%7B%5Cint_%7B%7Cx%7C%5Cleq1%7Df_n+d%5Coverline%7B%5Cmu%7D+%2B+%5Cint_%7B%7Cx%7C%3E1%7Df_n+d%5Coverline%7B%5Cmu%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;int_{|x|&#92;leq1}f_n d&#92;overline{&#92;mu} + &#92;int_{|x|&gt;1}f_n d&#92;overline{&#92;mu}}' title='{&#92;int_{|x|&#92;leq1}f_n d&#92;overline{&#92;mu} + &#92;int_{|x|&gt;1}f_n d&#92;overline{&#92;mu}}' class='latex' />, and the limit of each summand as <img src='http://s0.wp.com/latex.php?latex=%7Bn%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{n}' title='{n}' class='latex' /> goes to infinity is 0, we see <img src='http://s0.wp.com/latex.php?latex=%7B%5Clim_%7Bn+%5Crightarrow+%5Cinfty%7D+%5Cint+f_n+d%5Coverline%7B%5Cmu%7D+%3D0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;lim_{n &#92;rightarrow &#92;infty} &#92;int f_n d&#92;overline{&#92;mu} =0}' title='{&#92;lim_{n &#92;rightarrow &#92;infty} &#92;int f_n d&#92;overline{&#92;mu} =0}' class='latex' />. Since we defined <img src='http://s0.wp.com/latex.php?latex=%7B%5Clangle+g%2C+%5Cmu+%5Crangle%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;langle g, &#92;mu &#92;rangle}' title='{&#92;langle g, &#92;mu &#92;rangle}' class='latex' /> to be <img src='http://s0.wp.com/latex.php?latex=%7B%5Cint+g+d%5Coverline%7B%5Cmu%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;int g d&#92;overline{&#92;mu}}' title='{&#92;int g d&#92;overline{&#92;mu}}' class='latex' />, we see that <img src='http://s0.wp.com/latex.php?latex=%7B%5Clangle+f_n%2C+%5Cmu+%5Crangle+%5Crightarrow+0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;langle f_n, &#92;mu &#92;rangle &#92;rightarrow 0}' title='{&#92;langle f_n, &#92;mu &#92;rangle &#92;rightarrow 0}' class='latex' /> whenever <img src='http://s0.wp.com/latex.php?latex=%7Bf_n+%5Crightarrow+0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f_n &#92;rightarrow 0}' title='{f_n &#92;rightarrow 0}' class='latex' /> in the Schwartz space. Thus the map <img src='http://s0.wp.com/latex.php?latex=%7Bg+%5Crightarrow+%5Clangle+g%2C+%5Cmu+%5Crangle%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g &#92;rightarrow &#92;langle g, &#92;mu &#92;rangle}' title='{g &#92;rightarrow &#92;langle g, &#92;mu &#92;rangle}' class='latex' /> is continuous at 0, and since the map is linear, it&#8217;s continuous everywhere. Any Radon measure of polynomial growth induces a tempered distribution.</p>
<p>
<p><b> Exercise 31 </b></p>
<p> Remember, for a tempered distribution <img src='http://s0.wp.com/latex.php?latex=%7B%5Clambda%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;lambda}' title='{&#92;lambda}' class='latex' />, that we define <img src='http://s0.wp.com/latex.php?latex=%7B%5Clangle+f%2C+%5Cmathcal%7BF%7D+%5Clambda+%5Crangle+%3A%3D+%5Clangle+%5Cmathcal%7BF%7D%5E%2A+f%2C+%5Clambda+%5Crangle%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;langle f, &#92;mathcal{F} &#92;lambda &#92;rangle := &#92;langle &#92;mathcal{F}^* f, &#92;lambda &#92;rangle}' title='{&#92;langle f, &#92;mathcal{F} &#92;lambda &#92;rangle := &#92;langle &#92;mathcal{F}^* f, &#92;lambda &#92;rangle}' class='latex' /> for each function <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' /> in the Schwartz class. We define <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmathcal%7BF%7D%5E%2A+%5Clambda%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mathcal{F}^* &#92;lambda}' title='{&#92;mathcal{F}^* &#92;lambda}' class='latex' /> similarly. Also note that on the Schwartz space, that <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmathcal%7BF%7D%5E%7B-1%7D%3D%5Cmathcal%7BF%7D%5E%2A%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mathcal{F}^{-1}=&#92;mathcal{F}^*}' title='{&#92;mathcal{F}^{-1}=&#92;mathcal{F}^*}' class='latex' />. These exercises are very quick when one is familiar with Notes 2.</p>
<p>
i. We simply do the calculation. Given a tempered distribution <img src='http://s0.wp.com/latex.php?latex=%7B%5Clambda%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;lambda}' title='{&#92;lambda}' class='latex' />, then for any function <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' /> in the Schwartz space, we see
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Clangle+f%2C+%5Cmathcal%7BF%7D%5E%2A+%5Cmathcal%7BF%7D+%5Clambda+%5Crangle+%3D+%5Clangle+%5Cmathcal%7BF%7D+f%2C+%5Cmathcal%7BF%7D+%5Clambda+%5Crangle+%3D+%5Clangle+%5Cmathcal%7BF%7D%5E%2A+%5Cmathcal%7BF%7D+f%2C+%5Clambda+%5Crangle+%3D+%5Clangle+f%2C+%5Clambda+%5Crangle+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;langle f, &#92;mathcal{F}^* &#92;mathcal{F} &#92;lambda &#92;rangle = &#92;langle &#92;mathcal{F} f, &#92;mathcal{F} &#92;lambda &#92;rangle = &#92;langle &#92;mathcal{F}^* &#92;mathcal{F} f, &#92;lambda &#92;rangle = &#92;langle f, &#92;lambda &#92;rangle ' title='&#92;displaystyle  &#92;langle f, &#92;mathcal{F}^* &#92;mathcal{F} &#92;lambda &#92;rangle = &#92;langle &#92;mathcal{F} f, &#92;mathcal{F} &#92;lambda &#92;rangle = &#92;langle &#92;mathcal{F}^* &#92;mathcal{F} f, &#92;lambda &#92;rangle = &#92;langle f, &#92;lambda &#92;rangle ' class='latex' /></p>
<p> Thus <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmathcal%7BF%7D%5E%2A%5Cmathcal%7BF%7D+%5Clambda+%3D+%5Clambda%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mathcal{F}^*&#92;mathcal{F} &#92;lambda = &#92;lambda}' title='{&#92;mathcal{F}^*&#92;mathcal{F} &#92;lambda = &#92;lambda}' class='latex' />. An identical calculation shows <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmathcal%7BF%7D%5Cmathcal%7BF%7D%5E%2A+%5Clambda+%3D+%5Clambda%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mathcal{F}&#92;mathcal{F}^* &#92;lambda = &#92;lambda}' title='{&#92;mathcal{F}&#92;mathcal{F}^* &#92;lambda = &#92;lambda}' class='latex' />. Therefore, for each tempered distribution <img src='http://s0.wp.com/latex.php?latex=%7B%5Clambda%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;lambda}' title='{&#92;lambda}' class='latex' />, we see <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmathcal%7BF%7D%5E%2A%5Cmathcal%7BF%7D+%5Clambda+%3D+%5Cmathcal%7BF%7D%5Cmathcal%7BF%7D%5E%2A+%5Clambda+%3D+%5Clambda%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mathcal{F}^*&#92;mathcal{F} &#92;lambda = &#92;mathcal{F}&#92;mathcal{F}^* &#92;lambda = &#92;lambda}' title='{&#92;mathcal{F}^*&#92;mathcal{F} &#92;lambda = &#92;mathcal{F}&#92;mathcal{F}^* &#92;lambda = &#92;lambda}' class='latex' />.</p>
<p>
ii. Calculating the left-hand side gives us
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Clangle+g%2C+%5Cmathcal%7BF%7D%28f%5Clambda%29+%5Crangle+%3D+%5Clangle+%5Cmathcal%7BF%7D%5E%2A%28g%29%2C+f+%5Clambda+%5Crangle+%3D+%5Clangle+%5Coverline%7Bf%7D+%5Cmathcal%7BF%5E%2A%7D%28g%29%2C+%5Clambda+%5Crangle+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;langle g, &#92;mathcal{F}(f&#92;lambda) &#92;rangle = &#92;langle &#92;mathcal{F}^*(g), f &#92;lambda &#92;rangle = &#92;langle &#92;overline{f} &#92;mathcal{F^*}(g), &#92;lambda &#92;rangle ' title='&#92;displaystyle  &#92;langle g, &#92;mathcal{F}(f&#92;lambda) &#92;rangle = &#92;langle &#92;mathcal{F}^*(g), f &#92;lambda &#92;rangle = &#92;langle &#92;overline{f} &#92;mathcal{F^*}(g), &#92;lambda &#92;rangle ' class='latex' /></p>
<p> For any Schwartz function <img src='http://s0.wp.com/latex.php?latex=%7Bh%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{h}' title='{h}' class='latex' />, let <img src='http://s0.wp.com/latex.php?latex=%7B%5Ctilde%7Bh%7D%28x%29%3A%3D%5Coverline%7Bh%28-x%29%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;tilde{h}(x):=&#92;overline{h(-x)}}' title='{&#92;tilde{h}(x):=&#92;overline{h(-x)}}' class='latex' />. The right-hand side gives us
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Clangle+g%2C+%28%5Cmathcal%7BF%7D%5Clambda%29+%2A+%28%5Cmathcal%7BF%7Df%29+%5Crangle+%3D+%5Clangle+g+%2A+%5Cwidetilde%7B%5Cmathcal%7BF%7Df%7D+%2C+%5Cmathcal%7BF%7D%5Clambda+%5Crangle+%3D+%5Clangle+%5Cmathcal%7BF%7D%5E%2A+%5Cleft%28g+%2A+%5Cwidetilde%7B%5Cmathcal%7BF%7Df%7D+%5Cright%29%2C+%5Clambda+%5Crangle+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;langle g, (&#92;mathcal{F}&#92;lambda) * (&#92;mathcal{F}f) &#92;rangle = &#92;langle g * &#92;widetilde{&#92;mathcal{F}f} , &#92;mathcal{F}&#92;lambda &#92;rangle = &#92;langle &#92;mathcal{F}^* &#92;left(g * &#92;widetilde{&#92;mathcal{F}f} &#92;right), &#92;lambda &#92;rangle ' title='&#92;displaystyle  &#92;langle g, (&#92;mathcal{F}&#92;lambda) * (&#92;mathcal{F}f) &#92;rangle = &#92;langle g * &#92;widetilde{&#92;mathcal{F}f} , &#92;mathcal{F}&#92;lambda &#92;rangle = &#92;langle &#92;mathcal{F}^* &#92;left(g * &#92;widetilde{&#92;mathcal{F}f} &#92;right), &#92;lambda &#92;rangle ' class='latex' /></p>
<p> Now we have to deal with that messy expression. We can be clever and avoid having to see any messy integrals First we note that
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Cbegin%7Barray%7D%7Brcl%7D++%5Cwidetilde%7B%5Cmathcal%7BF%7Df%7D%28x%29+%26+%3D+%5Coverline%7B%5Cmathcal%7BF%7Df%28-x%29%7D+%3D+%5Coverline%7B+%5Cint+f%28%5Cxi%29+e%5E%7B2+%5Cpi+i+x+%5Ccdot+%5Cxi%7D+d%5Cxi+%7D+%3D+%5Coverline%7B%5Cmathcal%7BF%7D%5E%2Af%28x%29%7D+%3D+%5Coverline%7B%5Cmathcal%7BF%7D%5E%2Af%7D%28x%29+%5Cend%7Barray%7D+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;begin{array}{rcl}  &#92;widetilde{&#92;mathcal{F}f}(x) &amp; = &#92;overline{&#92;mathcal{F}f(-x)} = &#92;overline{ &#92;int f(&#92;xi) e^{2 &#92;pi i x &#92;cdot &#92;xi} d&#92;xi } = &#92;overline{&#92;mathcal{F}^*f(x)} = &#92;overline{&#92;mathcal{F}^*f}(x) &#92;end{array} ' title='&#92;displaystyle  &#92;begin{array}{rcl}  &#92;widetilde{&#92;mathcal{F}f}(x) &amp; = &#92;overline{&#92;mathcal{F}f(-x)} = &#92;overline{ &#92;int f(&#92;xi) e^{2 &#92;pi i x &#92;cdot &#92;xi} d&#92;xi } = &#92;overline{&#92;mathcal{F}^*f(x)} = &#92;overline{&#92;mathcal{F}^*f}(x) &#92;end{array} ' class='latex' /></p>
<p> Next thing we note, using the trick that complex conjugation and integration commutes. That is, for any two Schwartz functions <img src='http://s0.wp.com/latex.php?latex=%7Bh%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{h}' title='{h}' class='latex' /> and <img src='http://s0.wp.com/latex.php?latex=%7Bh%5E%5Cprime%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{h^&#92;prime}' title='{h^&#92;prime}' class='latex' />, we see
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Coverline%7Bh+%2A+h%5E%5Cprime%7D%28x%29+%3D+%5Coverline%7B+%5Cint+h%28y%29h%5E%5Cprime%28x-y%29+dy%7D+%3D+%5Cint+%5Coverline%7Bh%7D%28y%29%5Coverline%7Bh%5E%5Cprime%7D%28x-y%29+dy+%3D+%5Coverline%7Bh%7D+%2A+%5Coverline%7Bh%5E%5Cprime%7D%28x%29+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;overline{h * h^&#92;prime}(x) = &#92;overline{ &#92;int h(y)h^&#92;prime(x-y) dy} = &#92;int &#92;overline{h}(y)&#92;overline{h^&#92;prime}(x-y) dy = &#92;overline{h} * &#92;overline{h^&#92;prime}(x) ' title='&#92;displaystyle  &#92;overline{h * h^&#92;prime}(x) = &#92;overline{ &#92;int h(y)h^&#92;prime(x-y) dy} = &#92;int &#92;overline{h}(y)&#92;overline{h^&#92;prime}(x-y) dy = &#92;overline{h} * &#92;overline{h^&#92;prime}(x) ' class='latex' /></p>
<p> The last few things we note is that for two Schwartz function, <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmathcal%7BF%7D%28h+%2A+h%5E%5Cprime%29%28x%29%3D%28%5Cmathcal%7BF%7Dh%28x%29%29%28%5Cmathcal%7BF%7Dh%5E%5Cprime%28x%29%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mathcal{F}(h * h^&#92;prime)(x)=(&#92;mathcal{F}h(x))(&#92;mathcal{F}h^&#92;prime(x))}' title='{&#92;mathcal{F}(h * h^&#92;prime)(x)=(&#92;mathcal{F}h(x))(&#92;mathcal{F}h^&#92;prime(x))}' class='latex' />, and that for any Schwartz function, we have <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmathcal%7BF%7D%5E%2A%28h%29%3D%5Coverline%7B%5Cmathcal%7BF%7D%5Coverline%7Bh%7D%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mathcal{F}^*(h)=&#92;overline{&#92;mathcal{F}&#92;overline{h}}}' title='{&#92;mathcal{F}^*(h)=&#92;overline{&#92;mathcal{F}&#92;overline{h}}}' class='latex' />.</p>
<p>
We have all we need
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Cbegin%7Barray%7D%7Brcl%7D++%5Cmathcal%7BF%7D%5E%2A%28g+%2A+%5Cwidetilde%7B%5Cmathcal%7BF%7Df%7D%29+%26+%3D+%5Cmathcal%7BF%7D%5E%2A%28g+%2A+%5Coverline%7B%5Cmathcal%7BF%7D%5E%2A+f%7D%29+%3D+%5Coverline%7B%5Cmathcal%7BF%7D+%5Coverline%7B%28g+%2A+%5Cmathcal%7BF%7D%5Coverline%7Bf%7D%29%7D%7D+%5C%5C+%26+%3D+%5Coverline%7B%5Cmathcal%7BF%7D+%28%5Coverline%7Bg%7D+%2A+%5Coverline%7B%5Cmathcal%7BF%7D%5Coverline%7Bf%7D%7D%29%7D+%3D+%5Coverline%7B%5Cmathcal%7BF%7D+%28%5Coverline%7Bg%7D+%2A+%5Cmathcal%7BF%7D%5E%2Af%29%7D+%5C%5C+%26+%3D+%5Coverline%7B+%28%5Cmathcal%7BF%7D%5Coverline%7Bg%7D%29+%28%5Cmathcal%7BF%7D%5Cmathcal%7BF%7D%5E%2A+f%29%7D+%3D+%5Coverline%7B%28%5Cmathcal%7BF%7D%5Coverline%7Bg%7D%29f%7D+%5C%5C+%26+%3D+%5Coverline%7Bf%7D+%5Cmathcal%7BF%7D%5E%2A+g+%5Cend%7Barray%7D+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;begin{array}{rcl}  &#92;mathcal{F}^*(g * &#92;widetilde{&#92;mathcal{F}f}) &amp; = &#92;mathcal{F}^*(g * &#92;overline{&#92;mathcal{F}^* f}) = &#92;overline{&#92;mathcal{F} &#92;overline{(g * &#92;mathcal{F}&#92;overline{f})}} &#92;&#92; &amp; = &#92;overline{&#92;mathcal{F} (&#92;overline{g} * &#92;overline{&#92;mathcal{F}&#92;overline{f}})} = &#92;overline{&#92;mathcal{F} (&#92;overline{g} * &#92;mathcal{F}^*f)} &#92;&#92; &amp; = &#92;overline{ (&#92;mathcal{F}&#92;overline{g}) (&#92;mathcal{F}&#92;mathcal{F}^* f)} = &#92;overline{(&#92;mathcal{F}&#92;overline{g})f} &#92;&#92; &amp; = &#92;overline{f} &#92;mathcal{F}^* g &#92;end{array} ' title='&#92;displaystyle  &#92;begin{array}{rcl}  &#92;mathcal{F}^*(g * &#92;widetilde{&#92;mathcal{F}f}) &amp; = &#92;mathcal{F}^*(g * &#92;overline{&#92;mathcal{F}^* f}) = &#92;overline{&#92;mathcal{F} &#92;overline{(g * &#92;mathcal{F}&#92;overline{f})}} &#92;&#92; &amp; = &#92;overline{&#92;mathcal{F} (&#92;overline{g} * &#92;overline{&#92;mathcal{F}&#92;overline{f}})} = &#92;overline{&#92;mathcal{F} (&#92;overline{g} * &#92;mathcal{F}^*f)} &#92;&#92; &amp; = &#92;overline{ (&#92;mathcal{F}&#92;overline{g}) (&#92;mathcal{F}&#92;mathcal{F}^* f)} = &#92;overline{(&#92;mathcal{F}&#92;overline{g})f} &#92;&#92; &amp; = &#92;overline{f} &#92;mathcal{F}^* g &#92;end{array} ' class='latex' /></p>
<p> Thus we see that for all Schwartz functions <img src='http://s0.wp.com/latex.php?latex=%7Bg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g}' title='{g}' class='latex' />,
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Clangle+g%2C+%5Cmathcal%7BF%7D%28%5Clambda+f%29+%5Crangle+%3D+%5Clangle+g%2C+%28%5Cmathcal%7BF%7D%5Clambda%29+%2A+%28%5Cmathcal%7BF%7Df%29+%5Crangle+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;langle g, &#92;mathcal{F}(&#92;lambda f) &#92;rangle = &#92;langle g, (&#92;mathcal{F}&#92;lambda) * (&#92;mathcal{F}f) &#92;rangle ' title='&#92;displaystyle  &#92;langle g, &#92;mathcal{F}(&#92;lambda f) &#92;rangle = &#92;langle g, (&#92;mathcal{F}&#92;lambda) * (&#92;mathcal{F}f) &#92;rangle ' class='latex' /></p>
<p> Therefore, <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmathcal%7BF%7D%28%5Clambda+f%29%3D%28%5Cmathcal%7BF%7D%5Clambda%29+%2A+%28%5Cmathcal%7BF%7Df%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mathcal{F}(&#92;lambda f)=(&#92;mathcal{F}&#92;lambda) * (&#92;mathcal{F}f)}' title='{&#92;mathcal{F}(&#92;lambda f)=(&#92;mathcal{F}&#92;lambda) * (&#92;mathcal{F}f)}' class='latex' />.</p>
<p>
iii. Well, for any Schwartz function <img src='http://s0.wp.com/latex.php?latex=%7Bg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g}' title='{g}' class='latex' />,
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Clangle+g%2C+%5Cmathcal%7BF%7D%28%5Ctau_%7Bx_0%7D+%5Clambda%29+%5Crangle+%3D+%5Clangle+%5Cmathcal%7BF%7D%5E%2Ag%2C+%5Ctau_%7Bx_0%7D+%5Clambda+%5Crangle+%3D+%5Clangle+%5Ctau_%7B-x_0%7D%28%5Cmathcal%7BF%7D%5E%2Ag%29%2C+%5Clambda+%5Crangle+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;langle g, &#92;mathcal{F}(&#92;tau_{x_0} &#92;lambda) &#92;rangle = &#92;langle &#92;mathcal{F}^*g, &#92;tau_{x_0} &#92;lambda &#92;rangle = &#92;langle &#92;tau_{-x_0}(&#92;mathcal{F}^*g), &#92;lambda &#92;rangle ' title='&#92;displaystyle  &#92;langle g, &#92;mathcal{F}(&#92;tau_{x_0} &#92;lambda) &#92;rangle = &#92;langle &#92;mathcal{F}^*g, &#92;tau_{x_0} &#92;lambda &#92;rangle = &#92;langle &#92;tau_{-x_0}(&#92;mathcal{F}^*g), &#92;lambda &#92;rangle ' class='latex' /></p>
<p> For that Schwartz function <img src='http://s0.wp.com/latex.php?latex=%7Bg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g}' title='{g}' class='latex' />,
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%28%5Cmathcal%7BF%7D%5E%2Ag%29%28x%29+%3D+%5Cint+g%28%5Cxi%29+e%5E%7B2%5Cpi+i+%5Cxi+%5Ccdot+x%7D+d%5Cxi+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  (&#92;mathcal{F}^*g)(x) = &#92;int g(&#92;xi) e^{2&#92;pi i &#92;xi &#92;cdot x} d&#92;xi ' title='&#92;displaystyle  (&#92;mathcal{F}^*g)(x) = &#92;int g(&#92;xi) e^{2&#92;pi i &#92;xi &#92;cdot x} d&#92;xi ' class='latex' /></p>
<p> and thus,
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Cbegin%7Barray%7D%7Brcl%7D++%28%5Ctau_%7B-x_0%7D%28%5Cmathcal%7BF%7D%5E%2Ag%29%29%28x%29+%26+%3D+%28%5Cmathcal%7BF%7D%5E%2Ag%29%28x%2Bx_0%29+%3D+%5Cint+g%28%5Cxi%29+e%5E%7B2%5Cpi+i+%5Cxi+%5Ccdot+%28x%2Bx_0%29%7D+d%5Cxi+%5C%5C+%26+%3D+%5Cint+g%28%5Cxi%29+e_%7Bx_0%7D%28%5Cxi%29+e%5E%7B2%5Cpi+i+%5Cxi+%5Ccdot+x%7D+d%5Cxi+%3D+%5Cmathcal%7BF%7D%5E%2A%28e_%7Bx_0%7D+g%29%28x%29+%5Cend%7Barray%7D+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;begin{array}{rcl}  (&#92;tau_{-x_0}(&#92;mathcal{F}^*g))(x) &amp; = (&#92;mathcal{F}^*g)(x+x_0) = &#92;int g(&#92;xi) e^{2&#92;pi i &#92;xi &#92;cdot (x+x_0)} d&#92;xi &#92;&#92; &amp; = &#92;int g(&#92;xi) e_{x_0}(&#92;xi) e^{2&#92;pi i &#92;xi &#92;cdot x} d&#92;xi = &#92;mathcal{F}^*(e_{x_0} g)(x) &#92;end{array} ' title='&#92;displaystyle  &#92;begin{array}{rcl}  (&#92;tau_{-x_0}(&#92;mathcal{F}^*g))(x) &amp; = (&#92;mathcal{F}^*g)(x+x_0) = &#92;int g(&#92;xi) e^{2&#92;pi i &#92;xi &#92;cdot (x+x_0)} d&#92;xi &#92;&#92; &amp; = &#92;int g(&#92;xi) e_{x_0}(&#92;xi) e^{2&#92;pi i &#92;xi &#92;cdot x} d&#92;xi = &#92;mathcal{F}^*(e_{x_0} g)(x) &#92;end{array} ' class='latex' /></p>
<p> Therefore, for each Schwartz function <img src='http://s0.wp.com/latex.php?latex=%7Bg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g}' title='{g}' class='latex' />,
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Clangle+g%2C+%5Cmathcal%7BF%7D%28%5Ctau_%7Bx_0%7D+%5Clambda%29+%5Crangle+%3D+%5Clangle+%5Cmathcal%7BF%7D%5E%2A%28e_%7Bx_0%7D+g%29%2C+%5Clambda+%5Crangle+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;langle g, &#92;mathcal{F}(&#92;tau_{x_0} &#92;lambda) &#92;rangle = &#92;langle &#92;mathcal{F}^*(e_{x_0} g), &#92;lambda &#92;rangle ' title='&#92;displaystyle  &#92;langle g, &#92;mathcal{F}(&#92;tau_{x_0} &#92;lambda) &#92;rangle = &#92;langle &#92;mathcal{F}^*(e_{x_0} g), &#92;lambda &#92;rangle ' class='latex' /></p>
<p>
Now we note that given any <img src='http://s0.wp.com/latex.php?latex=%7Bx_0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x_0}' title='{x_0}' class='latex' />,
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Coverline%7Be_%7B-x_0%7D%28%5Cxi%29%7D%3D%5Coverline%7Be%5E%7B-2%5Cpi+i+x_0+%5Ccdot+%5Cxi%7D%7D+%3D+e%5E%7B2%5Cpi+i+x_0+%5Ccdot+%5Cxi%7D%3De_%7Bx_0%7D%28%5Cxi%29+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;overline{e_{-x_0}(&#92;xi)}=&#92;overline{e^{-2&#92;pi i x_0 &#92;cdot &#92;xi}} = e^{2&#92;pi i x_0 &#92;cdot &#92;xi}=e_{x_0}(&#92;xi) ' title='&#92;displaystyle  &#92;overline{e_{-x_0}(&#92;xi)}=&#92;overline{e^{-2&#92;pi i x_0 &#92;cdot &#92;xi}} = e^{2&#92;pi i x_0 &#92;cdot &#92;xi}=e_{x_0}(&#92;xi) ' class='latex' /></p>
<p> Thus, for any Schwartz function <img src='http://s0.wp.com/latex.php?latex=%7Bg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g}' title='{g}' class='latex' />,
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Clangle+g%2C+e_%7B-x_0%7D+%5Cmathcal%7BF%7D+%5Clambda+%5Crangle+%3D+%5Clangle+%5Coverline%7Be%7D_%7B-x_0%7D+g%2C+%5Cmathcal%7BF%7D+%5Clambda+%5Crangle+%3D+%5Clangle+e_%7Bx_0%7D+g%2C+%5Cmathcal%7BF%7D+%5Clambda+%5Crangle+%3D+%5Clangle+%5Cmathcal%7BF%7D%5E%2A%28e_%7Bx_0%7Dg%29%2C+%5Clambda+%5Crangle+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;langle g, e_{-x_0} &#92;mathcal{F} &#92;lambda &#92;rangle = &#92;langle &#92;overline{e}_{-x_0} g, &#92;mathcal{F} &#92;lambda &#92;rangle = &#92;langle e_{x_0} g, &#92;mathcal{F} &#92;lambda &#92;rangle = &#92;langle &#92;mathcal{F}^*(e_{x_0}g), &#92;lambda &#92;rangle ' title='&#92;displaystyle  &#92;langle g, e_{-x_0} &#92;mathcal{F} &#92;lambda &#92;rangle = &#92;langle &#92;overline{e}_{-x_0} g, &#92;mathcal{F} &#92;lambda &#92;rangle = &#92;langle e_{x_0} g, &#92;mathcal{F} &#92;lambda &#92;rangle = &#92;langle &#92;mathcal{F}^*(e_{x_0}g), &#92;lambda &#92;rangle ' class='latex' /></p>
<p> Thus, for any Schwartz function <img src='http://s0.wp.com/latex.php?latex=%7Bg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g}' title='{g}' class='latex' />, we see that
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Clangle+g%2C+%5Cmathcal%7BF%7D%28%5Ctau_%7Bx_0%7D%5Clambda%29+%5Crangle+%3D%5C+%5Clangle+g%2C+e_%7B-x_0%7D+%5Cmathcal%7BF%7D+%5Clambda+%5Crangle+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;langle g, &#92;mathcal{F}(&#92;tau_{x_0}&#92;lambda) &#92;rangle =&#92; &#92;langle g, e_{-x_0} &#92;mathcal{F} &#92;lambda &#92;rangle ' title='&#92;displaystyle  &#92;langle g, &#92;mathcal{F}(&#92;tau_{x_0}&#92;lambda) &#92;rangle =&#92; &#92;langle g, e_{-x_0} &#92;mathcal{F} &#92;lambda &#92;rangle ' class='latex' /></p>
<p> Therefore, <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmathcal%7BF%7D%28%5Ctau_%7Bx_0%7D%5Clambda%29%3De_%7B-x_0%7D%5Cmathcal%7BF%7D%5Clambda%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mathcal{F}(&#92;tau_{x_0}&#92;lambda)=e_{-x_0}&#92;mathcal{F}&#92;lambda}' title='{&#92;mathcal{F}(&#92;tau_{x_0}&#92;lambda)=e_{-x_0}&#92;mathcal{F}&#92;lambda}' class='latex' />.</p>
<p>
Similarly, for any Schwartz function <img src='http://s0.wp.com/latex.php?latex=%7Bg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g}' title='{g}' class='latex' />,
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Clangle+g%2C+%5Cmathcal%7BF%7D%28e_%7B%5Cxi_0%7D%5Clambda%29+%5Crangle+%3D+%5Clangle+%5Cmathcal%7BF%7D%5E%2Ag%2C+e_%7B%5Cxi_0%7D%5Clambda+%5Crangle+%3D+%5Clangle+%5Coverline%7Be%7D_%7B%5Cxi_0%7D+%5Cmathcal%7BF%7D%5E%2Ag%2C+%5Clambda+%5Crangle+%3D+%5Clangle+e_%7B-%5Cxi_0%7D+%5Cmathcal%7BF%7D%5E%2Ag%2C+%5Clambda+%5Crangle+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;langle g, &#92;mathcal{F}(e_{&#92;xi_0}&#92;lambda) &#92;rangle = &#92;langle &#92;mathcal{F}^*g, e_{&#92;xi_0}&#92;lambda &#92;rangle = &#92;langle &#92;overline{e}_{&#92;xi_0} &#92;mathcal{F}^*g, &#92;lambda &#92;rangle = &#92;langle e_{-&#92;xi_0} &#92;mathcal{F}^*g, &#92;lambda &#92;rangle ' title='&#92;displaystyle  &#92;langle g, &#92;mathcal{F}(e_{&#92;xi_0}&#92;lambda) &#92;rangle = &#92;langle &#92;mathcal{F}^*g, e_{&#92;xi_0}&#92;lambda &#92;rangle = &#92;langle &#92;overline{e}_{&#92;xi_0} &#92;mathcal{F}^*g, &#92;lambda &#92;rangle = &#92;langle e_{-&#92;xi_0} &#92;mathcal{F}^*g, &#92;lambda &#92;rangle ' class='latex' /></p>
<p>
On the other hand, for any Schwartz function <img src='http://s0.wp.com/latex.php?latex=%7Bg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g}' title='{g}' class='latex' />,
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Clangle+g%2C+%5Ctau_%7B%5Cxi_0%7D%5Cmathcal%7BF%7D%5Clambda+%5Crangle+%3D+%5Clangle+%5Ctau_%7B-%5Cxi_0%7Dg%2C+%5Cmathcal%7BF%7D+%5Clambda+%5Crangle+%3D+%5Clangle+%5Cmathcal%7BF%7D%5E%2A%28%5Ctau_%7B-%5Cxi_0%7Dg%29%2C+%5Clambda+%5Crangle+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;langle g, &#92;tau_{&#92;xi_0}&#92;mathcal{F}&#92;lambda &#92;rangle = &#92;langle &#92;tau_{-&#92;xi_0}g, &#92;mathcal{F} &#92;lambda &#92;rangle = &#92;langle &#92;mathcal{F}^*(&#92;tau_{-&#92;xi_0}g), &#92;lambda &#92;rangle ' title='&#92;displaystyle  &#92;langle g, &#92;tau_{&#92;xi_0}&#92;mathcal{F}&#92;lambda &#92;rangle = &#92;langle &#92;tau_{-&#92;xi_0}g, &#92;mathcal{F} &#92;lambda &#92;rangle = &#92;langle &#92;mathcal{F}^*(&#92;tau_{-&#92;xi_0}g), &#92;lambda &#92;rangle ' class='latex' /></p>
<p>
For any Schwartz function <img src='http://s0.wp.com/latex.php?latex=%7Bg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g}' title='{g}' class='latex' />,
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Cbegin%7Barray%7D%7Brcl%7D++%28%5Cmathcal%7BF%7D%5E%2A%28%5Ctau_%7B-%5Cxi_0%7Dg%29%29%28x%29+%26%3D+%5Cint+%28%5Ctau_%7B-%5Cxi_0%7Dg%29%28%5Cxi%29+e%5E%7B2+%5Cpi+i+x+%5Ccdot+%5Cxi%7Dd%5Cxi+%3D+%5Cint+g%28%5Cxi%2Bxi_0%29e%5E%7B2%5Cpi+i+x+%5Ccdot+%5Cxi%7D+d%5Cxi+%5C%5C+%26%3D+e%5E%7B-2%5Cpi+i+x+%5Ccdot+%5Cxi_0%7D+%5Cint+g%28%5Cxi%2Bxi_0%29e%5E%7B2%5Cpi+i+x+%5Ccdot+%28%5Cxi%2B%5Cxi_0%29%7D+d%5Cxi+%3D+e_%7B-%5Cxi_0%7D%28x%29+%5Cint+g%28%5Cxi%29+e%5E%7B2%5Cpi+i+x+%5Ccdot+%5Cxi%7D+d%5Cxi%5C%5C+%26%3D+e_%7B-%5Cxi_0%7D%28x%29+%28%5Cmathcal%7BF%7D%5E%2Ag%29%28x%29+%5Cend%7Barray%7D+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;begin{array}{rcl}  (&#92;mathcal{F}^*(&#92;tau_{-&#92;xi_0}g))(x) &amp;= &#92;int (&#92;tau_{-&#92;xi_0}g)(&#92;xi) e^{2 &#92;pi i x &#92;cdot &#92;xi}d&#92;xi = &#92;int g(&#92;xi+xi_0)e^{2&#92;pi i x &#92;cdot &#92;xi} d&#92;xi &#92;&#92; &amp;= e^{-2&#92;pi i x &#92;cdot &#92;xi_0} &#92;int g(&#92;xi+xi_0)e^{2&#92;pi i x &#92;cdot (&#92;xi+&#92;xi_0)} d&#92;xi = e_{-&#92;xi_0}(x) &#92;int g(&#92;xi) e^{2&#92;pi i x &#92;cdot &#92;xi} d&#92;xi&#92;&#92; &amp;= e_{-&#92;xi_0}(x) (&#92;mathcal{F}^*g)(x) &#92;end{array} ' title='&#92;displaystyle  &#92;begin{array}{rcl}  (&#92;mathcal{F}^*(&#92;tau_{-&#92;xi_0}g))(x) &amp;= &#92;int (&#92;tau_{-&#92;xi_0}g)(&#92;xi) e^{2 &#92;pi i x &#92;cdot &#92;xi}d&#92;xi = &#92;int g(&#92;xi+xi_0)e^{2&#92;pi i x &#92;cdot &#92;xi} d&#92;xi &#92;&#92; &amp;= e^{-2&#92;pi i x &#92;cdot &#92;xi_0} &#92;int g(&#92;xi+xi_0)e^{2&#92;pi i x &#92;cdot (&#92;xi+&#92;xi_0)} d&#92;xi = e_{-&#92;xi_0}(x) &#92;int g(&#92;xi) e^{2&#92;pi i x &#92;cdot &#92;xi} d&#92;xi&#92;&#92; &amp;= e_{-&#92;xi_0}(x) (&#92;mathcal{F}^*g)(x) &#92;end{array} ' class='latex' /></p>
<p> Thus, <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmathcal%7BF%7D%5E%2A%28%5Ctau_%7B-%5Cxi_0%7Dg%29%3De_%7B-%5Cxi_0%7D%5Cmathcal%7BF%7D%5E%2Ag%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mathcal{F}^*(&#92;tau_{-&#92;xi_0}g)=e_{-&#92;xi_0}&#92;mathcal{F}^*g}' title='{&#92;mathcal{F}^*(&#92;tau_{-&#92;xi_0}g)=e_{-&#92;xi_0}&#92;mathcal{F}^*g}' class='latex' />. So for any Schwartz function <img src='http://s0.wp.com/latex.php?latex=%7Bg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g}' title='{g}' class='latex' />,
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Clangle+g%2C+%5Cmathcal%7BF%7D%28e_%7B%5Cxi_0%7D%5Clambda%29+%5Crangle+%3D+%5Clangle+e_%7B%5Cxi_0%7D%5Cmathcal%7BF%7D%5E%2Ag%2C+%5Clambda+%5Crangle+%3D+%5Clangle+%5Cmathcal%7BF%7D%5E%2A%28%5Ctau_%7B-%5Cxi_0%7Dg%29%2C+%5Clambda+%5Crangle+%3D+%5Clangle+g%2C+%5Ctau_%7B%5Cxi_0%7D%5Cmathcal%7BF%7D%5Clambda+%5Crangle+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;langle g, &#92;mathcal{F}(e_{&#92;xi_0}&#92;lambda) &#92;rangle = &#92;langle e_{&#92;xi_0}&#92;mathcal{F}^*g, &#92;lambda &#92;rangle = &#92;langle &#92;mathcal{F}^*(&#92;tau_{-&#92;xi_0}g), &#92;lambda &#92;rangle = &#92;langle g, &#92;tau_{&#92;xi_0}&#92;mathcal{F}&#92;lambda &#92;rangle ' title='&#92;displaystyle  &#92;langle g, &#92;mathcal{F}(e_{&#92;xi_0}&#92;lambda) &#92;rangle = &#92;langle e_{&#92;xi_0}&#92;mathcal{F}^*g, &#92;lambda &#92;rangle = &#92;langle &#92;mathcal{F}^*(&#92;tau_{-&#92;xi_0}g), &#92;lambda &#92;rangle = &#92;langle g, &#92;tau_{&#92;xi_0}&#92;mathcal{F}&#92;lambda &#92;rangle ' class='latex' /></p>
<p> Therefore <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmathcal%7BF%7D%28e_%7B%5Cxi_0%7D%5Clambda%29%3D%5Ctau_%7B%5Cxi_0%7D%5Cmathcal%7BF%7D%5Clambda%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mathcal{F}(e_{&#92;xi_0}&#92;lambda)=&#92;tau_{&#92;xi_0}&#92;mathcal{F}&#92;lambda}' title='{&#92;mathcal{F}(e_{&#92;xi_0}&#92;lambda)=&#92;tau_{&#92;xi_0}&#92;mathcal{F}&#92;lambda}' class='latex' />.</p>
<p>
iv. First note, that <img src='http://s0.wp.com/latex.php?latex=%7BL%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{L}' title='{L}' class='latex' /> is a linear operator on <img src='http://s0.wp.com/latex.php?latex=%7B%7B%5Cmathbb+R%7D%5Ed%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{{&#92;mathbb R}^d}' title='{{&#92;mathbb R}^d}' class='latex' />, and as a result, the adjoint is simply the transpose of <img src='http://s0.wp.com/latex.php?latex=%7BL%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{L}' title='{L}' class='latex' />. In general, our life is greatly simplified, since <img src='http://s0.wp.com/latex.php?latex=%7BL%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{L}' title='{L}' class='latex' /> is real, and for real invertible matrices, taking the adjoint and taking the inverse are operations that commute. Also note that the determinant of the transpose is the same as the determinant of the original operator. Well, for any Schwartz function <img src='http://s0.wp.com/latex.php?latex=%7Bg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g}' title='{g}' class='latex' />,
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Cbegin%7Barray%7D%7Brcl%7D++%5Clangle+g%2C+%5Cfrac%7B1%7D%7B%7C%5Cdet+L%7C%7D+%28%5Cmathcal%7BF%7D%5Clambda%29+%5Ccirc+%7B%28L%5E%2A%29%7D%5E%7B-1%7D+%5Crangle+%26+%3D+%5Cfrac%7B1%7D%7B%7C%5Cdet+L%7C%7D%5Clangle+g%2C+%28%5Cmathcal%7BF%7D%5Clambda%29+%5Ccirc+%7B%28L%5E%2A%29%7D%5E%7B-1%7D+%5Crangle+%3D+%5Cfrac%7B1%7D%7B%7C%5Cdet+L%7C%7D+%5Cfrac%7B1%7D%7B%7C%5Cdet+%7B%28L%5E%2A%29%7D%5E%7B-1%7D%7C%7D+%5Clangle+g+%5Ccirc+L%5E%2A%2C+%5Cmathcal%7BF%7D%5Clambda+%5Crangle+%5C%5C+%26+%3D+%5Cfrac%7B%7C%5Cdet+L%5E%2A%7C%7D%7B%7C%5Cdet+L%7C%7D+%5Clangle+g+%5Ccirc+L%5E%2A%2C+%5Cmathcal%7BF%7D%5Clambda+%5Crangle+%3D+%5Clangle+g+%5Ccirc+L%5E%2A%2C+%5Cmathcal%7BF%7D+%5Clambda+%5Crangle+%3D+%5Clangle+%5Cmathcal%7BF%7D%5E%2A%28g+%5Ccirc+L%5E%2A%29%2C+%5Clambda+%5Crangle+%5Cend%7Barray%7D+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;begin{array}{rcl}  &#92;langle g, &#92;frac{1}{|&#92;det L|} (&#92;mathcal{F}&#92;lambda) &#92;circ {(L^*)}^{-1} &#92;rangle &amp; = &#92;frac{1}{|&#92;det L|}&#92;langle g, (&#92;mathcal{F}&#92;lambda) &#92;circ {(L^*)}^{-1} &#92;rangle = &#92;frac{1}{|&#92;det L|} &#92;frac{1}{|&#92;det {(L^*)}^{-1}|} &#92;langle g &#92;circ L^*, &#92;mathcal{F}&#92;lambda &#92;rangle &#92;&#92; &amp; = &#92;frac{|&#92;det L^*|}{|&#92;det L|} &#92;langle g &#92;circ L^*, &#92;mathcal{F}&#92;lambda &#92;rangle = &#92;langle g &#92;circ L^*, &#92;mathcal{F} &#92;lambda &#92;rangle = &#92;langle &#92;mathcal{F}^*(g &#92;circ L^*), &#92;lambda &#92;rangle &#92;end{array} ' title='&#92;displaystyle  &#92;begin{array}{rcl}  &#92;langle g, &#92;frac{1}{|&#92;det L|} (&#92;mathcal{F}&#92;lambda) &#92;circ {(L^*)}^{-1} &#92;rangle &amp; = &#92;frac{1}{|&#92;det L|}&#92;langle g, (&#92;mathcal{F}&#92;lambda) &#92;circ {(L^*)}^{-1} &#92;rangle = &#92;frac{1}{|&#92;det L|} &#92;frac{1}{|&#92;det {(L^*)}^{-1}|} &#92;langle g &#92;circ L^*, &#92;mathcal{F}&#92;lambda &#92;rangle &#92;&#92; &amp; = &#92;frac{|&#92;det L^*|}{|&#92;det L|} &#92;langle g &#92;circ L^*, &#92;mathcal{F}&#92;lambda &#92;rangle = &#92;langle g &#92;circ L^*, &#92;mathcal{F} &#92;lambda &#92;rangle = &#92;langle &#92;mathcal{F}^*(g &#92;circ L^*), &#92;lambda &#92;rangle &#92;end{array} ' class='latex' /></p>
<p>
Computing form the other direction, we see
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Clangle+g%2C+%5Cmathcal%7BF%7D%28%5Clambda+%5Ccirc+L%29+%5Crangle+%3D+%5Clangle+%5Cmathcal%7BF%7D%5E%2Ag%2C+%5Clambda+%5Ccirc+L+%5Crangle+%3D+%5Cfrac%7B1%7D%7B%7C%5Cdet+L%7C%7D+%5Clangle+%28%5Cmathcal%7BF%7D%5E%2Ag%29+%5Ccirc+L%5E%7B-1%7D%2C+%5Clambda+%5Crangle+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;langle g, &#92;mathcal{F}(&#92;lambda &#92;circ L) &#92;rangle = &#92;langle &#92;mathcal{F}^*g, &#92;lambda &#92;circ L &#92;rangle = &#92;frac{1}{|&#92;det L|} &#92;langle (&#92;mathcal{F}^*g) &#92;circ L^{-1}, &#92;lambda &#92;rangle ' title='&#92;displaystyle  &#92;langle g, &#92;mathcal{F}(&#92;lambda &#92;circ L) &#92;rangle = &#92;langle &#92;mathcal{F}^*g, &#92;lambda &#92;circ L &#92;rangle = &#92;frac{1}{|&#92;det L|} &#92;langle (&#92;mathcal{F}^*g) &#92;circ L^{-1}, &#92;lambda &#92;rangle ' class='latex' /></p>
<p> We should first note, that direct calculation shows <img src='http://s0.wp.com/latex.php?latex=%7B%28%5Cmathcal%7BF%7D%5E%2Ag%29+%5Ccirc+L%5E%7B-1%7D%3D+%5Cmathcal%7BF%7D%5E%2A%28g+%5Ccirc+L%5E%7B-1%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{(&#92;mathcal{F}^*g) &#92;circ L^{-1}= &#92;mathcal{F}^*(g &#92;circ L^{-1})}' title='{(&#92;mathcal{F}^*g) &#92;circ L^{-1}= &#92;mathcal{F}^*(g &#92;circ L^{-1})}' class='latex' />.</p>
<p>
From Exercise from Notes 2, we know how the Fourier Transform under changes of variables. In particular, if <img src='http://s0.wp.com/latex.php?latex=%7BK%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{K}' title='{K}' class='latex' /> is an invertible linear transformation, and <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' /> is a Schwartz function, then
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Cmathcal%7BF%7D%28f+%5Ccirc+K%29+%3D+%5Cfrac%7B1%7D%7B%7C%5Cdet+K%7C%7D+%28%5Cmathcal%7BF%7Df%29+%5Ccirc+%7B%28K%5E%2A%29%7D%5E%7B-1%7D+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;mathcal{F}(f &#92;circ K) = &#92;frac{1}{|&#92;det K|} (&#92;mathcal{F}f) &#92;circ {(K^*)}^{-1} ' title='&#92;displaystyle  &#92;mathcal{F}(f &#92;circ K) = &#92;frac{1}{|&#92;det K|} (&#92;mathcal{F}f) &#92;circ {(K^*)}^{-1} ' class='latex' /></p>
<p> We again use the identity <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmathcal%7BF%7D%5E%2Af+%3D+%5Coverline%7B%5Cmathcal%7BF%7D%5Coverline%7Bf%7D%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mathcal{F}^*f = &#92;overline{&#92;mathcal{F}&#92;overline{f}}}' title='{&#92;mathcal{F}^*f = &#92;overline{&#92;mathcal{F}&#92;overline{f}}}' class='latex' /> for each Schwartz function to see for any <img src='http://s0.wp.com/latex.php?latex=%7Bx+%5Cin+%7B%5Cmathbb+R%7D%5Ed%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x &#92;in {&#92;mathbb R}^d}' title='{x &#92;in {&#92;mathbb R}^d}' class='latex' />
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Cbegin%7Barray%7D%7Brcl%7D++%28%5Cmathcal%7BF%7D%5E%2A%28f+%5Ccirc+K%29%29+%26+%3D+%5Coverline%7B+%5Cmathcal%7BF%7D%5Coverline%7B%28f+%5Ccirc+K%7D%29%7D+%3D+%5Coverline%7B%5Cmathcal%7BF%7D%28+%5Coverline%7Bf%7D+%5Ccirc+K%29%7D+%5C%5C+%26+%3D+%5Coverline%7B%5Cfrac%7B1%7D%7B%7C%5Cdet+K%7C%7D+%28%5Cmathcal%7BF%7D%5Coverline%7Bf%7D%29+%5Ccirc+%7B%28K%5E%2A%29%7D%5E%7B-1%7D%7D+%3D+%5Cfrac%7B1%7D%7B%7C%5Cdet+K%7C%7D+%28%5Coverline%7B%5Cmathcal%7BF%7D%5Coverline%7Bf%7D%7D%29+%5Ccirc+%7B%28K%5E%2A%29%7D%5E%7B-1%7D+%5C%5C+%26+%3D+%5Cfrac%7B1%7D%7B%7C%5Cdet+K%7C%7D+%28%5Cmathcal%7BF%7D%5E%2Af%29+%5Ccirc+%7B%28K%5E%2A%29%7D%5E%7B-1%7D+%5Cend%7Barray%7D+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;begin{array}{rcl}  (&#92;mathcal{F}^*(f &#92;circ K)) &amp; = &#92;overline{ &#92;mathcal{F}&#92;overline{(f &#92;circ K})} = &#92;overline{&#92;mathcal{F}( &#92;overline{f} &#92;circ K)} &#92;&#92; &amp; = &#92;overline{&#92;frac{1}{|&#92;det K|} (&#92;mathcal{F}&#92;overline{f}) &#92;circ {(K^*)}^{-1}} = &#92;frac{1}{|&#92;det K|} (&#92;overline{&#92;mathcal{F}&#92;overline{f}}) &#92;circ {(K^*)}^{-1} &#92;&#92; &amp; = &#92;frac{1}{|&#92;det K|} (&#92;mathcal{F}^*f) &#92;circ {(K^*)}^{-1} &#92;end{array} ' title='&#92;displaystyle  &#92;begin{array}{rcl}  (&#92;mathcal{F}^*(f &#92;circ K)) &amp; = &#92;overline{ &#92;mathcal{F}&#92;overline{(f &#92;circ K})} = &#92;overline{&#92;mathcal{F}( &#92;overline{f} &#92;circ K)} &#92;&#92; &amp; = &#92;overline{&#92;frac{1}{|&#92;det K|} (&#92;mathcal{F}&#92;overline{f}) &#92;circ {(K^*)}^{-1}} = &#92;frac{1}{|&#92;det K|} (&#92;overline{&#92;mathcal{F}&#92;overline{f}}) &#92;circ {(K^*)}^{-1} &#92;&#92; &amp; = &#92;frac{1}{|&#92;det K|} (&#92;mathcal{F}^*f) &#92;circ {(K^*)}^{-1} &#92;end{array} ' class='latex' /></p>
<p>
So returning to our first calculation, we see
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Cbegin%7Barray%7D%7Brcl%7D++%5Clangle+g%2C+%5Cfrac%7B1%7D%7B%7C%5Cdet+L%7C%7D%28%5Cmathcal%7BF%7D%5Clambda%29+%5Ccirc+%7B%28L%5E%2A%29%7D%5E%7B-1%7D+%5Crangle+%26+%3D+%5Clangle+%5Cmathcal%7BF%7D%5E%2A%28g+%5Ccirc+L%5E%2A%29%2C+%5Clambda+%5Crangle+%3D+%5Clangle+%5Cfrac%7B1%7D%7B%7C%5Cdet+L%5E%2A%7C%7D+%28%5Cmathcal%7BF%7D%5E%2Ag%29+%5Ccirc+%7B%28%7B%28L%5E%2A%29%7D%5E%2A%29%5E%7B-1%7D%7D%2C+%5Clambda+%5Crangle+%5C%5C+%26+%3D+%5Cfrac%7B1%7D%7B%7C%5Cdet+L%7C%7D+%5Clangle+%28%5Cmathcal%7BF%7D%5E%2Ag%29+%5Ccirc+L%5E%7B-1%7D%2C+%5Clambda+%5Crangle+%3D+%5Clangle+g%2C+%5Cmathcal%7BF%7D%28%5Clambda+%5Ccirc+L%29+%5Crangle+%5Cend%7Barray%7D+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;begin{array}{rcl}  &#92;langle g, &#92;frac{1}{|&#92;det L|}(&#92;mathcal{F}&#92;lambda) &#92;circ {(L^*)}^{-1} &#92;rangle &amp; = &#92;langle &#92;mathcal{F}^*(g &#92;circ L^*), &#92;lambda &#92;rangle = &#92;langle &#92;frac{1}{|&#92;det L^*|} (&#92;mathcal{F}^*g) &#92;circ {({(L^*)}^*)^{-1}}, &#92;lambda &#92;rangle &#92;&#92; &amp; = &#92;frac{1}{|&#92;det L|} &#92;langle (&#92;mathcal{F}^*g) &#92;circ L^{-1}, &#92;lambda &#92;rangle = &#92;langle g, &#92;mathcal{F}(&#92;lambda &#92;circ L) &#92;rangle &#92;end{array} ' title='&#92;displaystyle  &#92;begin{array}{rcl}  &#92;langle g, &#92;frac{1}{|&#92;det L|}(&#92;mathcal{F}&#92;lambda) &#92;circ {(L^*)}^{-1} &#92;rangle &amp; = &#92;langle &#92;mathcal{F}^*(g &#92;circ L^*), &#92;lambda &#92;rangle = &#92;langle &#92;frac{1}{|&#92;det L^*|} (&#92;mathcal{F}^*g) &#92;circ {({(L^*)}^*)^{-1}}, &#92;lambda &#92;rangle &#92;&#92; &amp; = &#92;frac{1}{|&#92;det L|} &#92;langle (&#92;mathcal{F}^*g) &#92;circ L^{-1}, &#92;lambda &#92;rangle = &#92;langle g, &#92;mathcal{F}(&#92;lambda &#92;circ L) &#92;rangle &#92;end{array} ' class='latex' /></p>
<p>
We have obtained our desired result. <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmathcal%7BF%7D%28%5Clambda+%5Ccirc+L%29+%3D+%5Cfrac%7B1%7D%7B%7C%5Cdet+L%7C%7D+%28%5Cmathcal%7BF%7D%5Clambda%29+%5Ccirc+%7B%28L%5E%2A%29%7D%5E%7B-1%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mathcal{F}(&#92;lambda &#92;circ L) = &#92;frac{1}{|&#92;det L|} (&#92;mathcal{F}&#92;lambda) &#92;circ {(L^*)}^{-1}}' title='{&#92;mathcal{F}(&#92;lambda &#92;circ L) = &#92;frac{1}{|&#92;det L|} (&#92;mathcal{F}&#92;lambda) &#92;circ {(L^*)}^{-1}}' class='latex' /></p>
<p>
v. Exercise 23 and 24 of Notes 2 are key here. The former says that for any Schwartz function <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' />,
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%28%5Cfrac%7B%5Cpartial%7D%7B%5Cpartial+%5Cxi_j%7D%5Cmathcal%7BF%7Df%29%28%5Cxi%29+%3D+-2%5Cpi+i+%28%5Cmathcal%7BF%7D%28x_j+f%29%29%28%5Cxi%29+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  (&#92;frac{&#92;partial}{&#92;partial &#92;xi_j}&#92;mathcal{F}f)(&#92;xi) = -2&#92;pi i (&#92;mathcal{F}(x_j f))(&#92;xi) ' title='&#92;displaystyle  (&#92;frac{&#92;partial}{&#92;partial &#92;xi_j}&#92;mathcal{F}f)(&#92;xi) = -2&#92;pi i (&#92;mathcal{F}(x_j f))(&#92;xi) ' class='latex' /></p>
<p> Similarly, the latter exercise says that for any Schwartz function <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' />,
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Cmathcal%7BF%7D%28%5Cfrac%7B%5Cpartial+f%7D%7B%5Cpartial+x_j%7D%29%28%5Cxi%29+%3D+2%5Cpi+i+%5Cxi_j+%28%5Cmathcal%7BF%7Df%29%28%5Cxi%29+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;mathcal{F}(&#92;frac{&#92;partial f}{&#92;partial x_j})(&#92;xi) = 2&#92;pi i &#92;xi_j (&#92;mathcal{F}f)(&#92;xi) ' title='&#92;displaystyle  &#92;mathcal{F}(&#92;frac{&#92;partial f}{&#92;partial x_j})(&#92;xi) = 2&#92;pi i &#92;xi_j (&#92;mathcal{F}f)(&#92;xi) ' class='latex' /></p>
<p> Using the identity, <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmathcal%7BF%7D%5E%2Af%3D%5Coverline%7B%5Cmathcal%7BF%7D%5Coverline%7Bf%7D%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mathcal{F}^*f=&#92;overline{&#92;mathcal{F}&#92;overline{f}}}' title='{&#92;mathcal{F}^*f=&#92;overline{&#92;mathcal{F}&#92;overline{f}}}' class='latex' />, we see that
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%28%5Cfrac%7B%5Cpartial%7D%7B%5Cpartial+%5Cxi_j%7D%5Cmathcal%7BF%7D%5E%2Af%29%28%5Cxi%29+%3D+2%5Cpi+i+%28%5Cmathcal%7BF%7D%5E%2A%28x_j+f%29%29%28%5Cxi%29+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  (&#92;frac{&#92;partial}{&#92;partial &#92;xi_j}&#92;mathcal{F}^*f)(&#92;xi) = 2&#92;pi i (&#92;mathcal{F}^*(x_j f))(&#92;xi) ' title='&#92;displaystyle  (&#92;frac{&#92;partial}{&#92;partial &#92;xi_j}&#92;mathcal{F}^*f)(&#92;xi) = 2&#92;pi i (&#92;mathcal{F}^*(x_j f))(&#92;xi) ' class='latex' /></p>
<p> and
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Cmathcal%7BF%7D%5E%2A%28%5Cfrac%7B%5Cpartial+f%7D%7B%5Cpartial+x_j%7D%29%28%5Cxi%29+%3D+-+2%5Cpi+i+%5Cxi_j+%28%5Cmathcal%7BF%7D%5E%2Af%29%28%5Cxi%29+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;mathcal{F}^*(&#92;frac{&#92;partial f}{&#92;partial x_j})(&#92;xi) = - 2&#92;pi i &#92;xi_j (&#92;mathcal{F}^*f)(&#92;xi) ' title='&#92;displaystyle  &#92;mathcal{F}^*(&#92;frac{&#92;partial f}{&#92;partial x_j})(&#92;xi) = - 2&#92;pi i &#92;xi_j (&#92;mathcal{F}^*f)(&#92;xi) ' class='latex' /></p>
<p>
So given any Schwartz function <img src='http://s0.wp.com/latex.php?latex=%7Bg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g}' title='{g}' class='latex' /> and distribution <img src='http://s0.wp.com/latex.php?latex=%7B%5Clambda%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;lambda}' title='{&#92;lambda}' class='latex' />, we see
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Cbegin%7Barray%7D%7Brcl%7D++%5Clangle+g%2C+%5Cmathcal%7BF%7D%28%5Cfrac%7B%5Cpartial%7D%7B%5Cpartial+x_j%7D+%5Clambda%29+%5Crangle+%26%3D+%5Clangle+%5Cmathcal%7BF%7D%5E%2Ag%2C+%5Cfrac%7B%5Cpartial%7D%7B%5Cpartial+x_j%7D+%5Clambda+%5Crangle+%3D+-+%5Clangle+%5Cfrac%7B%5Cpartial%7D%7B%5Cpartial+x_j%7D+%5Cmathcal%7BF%7D%5E%2Ag%2C+%5Clambda+%5Crangle+%5C%5C+%26+%3D%5Clangle+-2%5Cpi+i+%5Cmathcal%7BF%7D%5E%2A%28x_j+g%29%2C+%5Clambda+%5Crangle+%3D+%5Clangle+%5Cmathcal%7BF%7D%5E%2A%28-2%5Cpi+i+x_j+g%29%2C+%5Clambda+%5Crangle+%5C%5C+%26+%3D+%5Clangle+-2%5Cpi+i+x_j+g%2C+%5Cmathcal%7BF%7D+%5Clambda+%5Crangle+%3D+%5Clangle+g%2C+2%5Cpi+i+x_j+%5Cmathcal%7BF%7D+%5Clambda+%5Crangle+%5Cend%7Barray%7D+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;begin{array}{rcl}  &#92;langle g, &#92;mathcal{F}(&#92;frac{&#92;partial}{&#92;partial x_j} &#92;lambda) &#92;rangle &amp;= &#92;langle &#92;mathcal{F}^*g, &#92;frac{&#92;partial}{&#92;partial x_j} &#92;lambda &#92;rangle = - &#92;langle &#92;frac{&#92;partial}{&#92;partial x_j} &#92;mathcal{F}^*g, &#92;lambda &#92;rangle &#92;&#92; &amp; =&#92;langle -2&#92;pi i &#92;mathcal{F}^*(x_j g), &#92;lambda &#92;rangle = &#92;langle &#92;mathcal{F}^*(-2&#92;pi i x_j g), &#92;lambda &#92;rangle &#92;&#92; &amp; = &#92;langle -2&#92;pi i x_j g, &#92;mathcal{F} &#92;lambda &#92;rangle = &#92;langle g, 2&#92;pi i x_j &#92;mathcal{F} &#92;lambda &#92;rangle &#92;end{array} ' title='&#92;displaystyle  &#92;begin{array}{rcl}  &#92;langle g, &#92;mathcal{F}(&#92;frac{&#92;partial}{&#92;partial x_j} &#92;lambda) &#92;rangle &amp;= &#92;langle &#92;mathcal{F}^*g, &#92;frac{&#92;partial}{&#92;partial x_j} &#92;lambda &#92;rangle = - &#92;langle &#92;frac{&#92;partial}{&#92;partial x_j} &#92;mathcal{F}^*g, &#92;lambda &#92;rangle &#92;&#92; &amp; =&#92;langle -2&#92;pi i &#92;mathcal{F}^*(x_j g), &#92;lambda &#92;rangle = &#92;langle &#92;mathcal{F}^*(-2&#92;pi i x_j g), &#92;lambda &#92;rangle &#92;&#92; &amp; = &#92;langle -2&#92;pi i x_j g, &#92;mathcal{F} &#92;lambda &#92;rangle = &#92;langle g, 2&#92;pi i x_j &#92;mathcal{F} &#92;lambda &#92;rangle &#92;end{array} ' class='latex' /></p>
<p> Therefore <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmathcal%7BF%7D%28%5Cfrac%7B%5Cpartial%7D%7B%5Cpartial+x_j%7D+%5Clambda%29+%3D+2%5Cpi+i+x_j+%5Cmathcal%7BF%7D%5Clambda%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mathcal{F}(&#92;frac{&#92;partial}{&#92;partial x_j} &#92;lambda) = 2&#92;pi i x_j &#92;mathcal{F}&#92;lambda}' title='{&#92;mathcal{F}(&#92;frac{&#92;partial}{&#92;partial x_j} &#92;lambda) = 2&#92;pi i x_j &#92;mathcal{F}&#92;lambda}' class='latex' />.</p>
<p>
Similarly, given any Schwartz function <img src='http://s0.wp.com/latex.php?latex=%7Bg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g}' title='{g}' class='latex' />, we see
<p align="center"><img src='http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%5Cbegin%7Barray%7D%7Brcl%7D++%5Clangle+g%2C+%5Cmathcal%7BF%7D%28-2%5Cpi+i+x_j+%5Clambda%29+%5Crangle+%26%3D+%5Clangle+%5Cmathcal%7BF%7D%5E%2Ag%2C+-2%5Cpi+i+x_j+%5Clambda+%5Crangle+%3D+%5Clangle+2%5Cpi+i+x_j+%5Cmathcal%7BF%7D%5E%2Ag%2C+%5Clambda+%5Crangle+%5C%5C+%26+%3D+-+%5Clangle+-2%5Cpi+i+x_j+%5Cmathcal%7BF%7D%5E%2Ag%2C+%5Clambda+%5Crangle+%3D+-+%5Clangle+%5Cmathcal%7BF%7D%5E%2A%28%5Cfrac%7B%5Cpartial+g%7D%7B%5Cpartial+x_j%7D%29%2C+%5Clambda+%5Crangle+%5C%5C+%26+%3D+-+%5Clangle+%5Cfrac%7B%5Cpartial+g%7D%7B%5Cpartial+x_j%7D%2C+%5Cmathcal%7BF%7D%5Clambda+%5Crangle+%3D+%5Clangle+g%2C+%5Cfrac%7B%5Cpartial%7D%7B%5Cpartial+x_j%7D+%28%5Cmathcal%7BF%7D%5Clambda%29+%5Crangle+%5Cend%7Barray%7D+&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='&#92;displaystyle  &#92;begin{array}{rcl}  &#92;langle g, &#92;mathcal{F}(-2&#92;pi i x_j &#92;lambda) &#92;rangle &amp;= &#92;langle &#92;mathcal{F}^*g, -2&#92;pi i x_j &#92;lambda &#92;rangle = &#92;langle 2&#92;pi i x_j &#92;mathcal{F}^*g, &#92;lambda &#92;rangle &#92;&#92; &amp; = - &#92;langle -2&#92;pi i x_j &#92;mathcal{F}^*g, &#92;lambda &#92;rangle = - &#92;langle &#92;mathcal{F}^*(&#92;frac{&#92;partial g}{&#92;partial x_j}), &#92;lambda &#92;rangle &#92;&#92; &amp; = - &#92;langle &#92;frac{&#92;partial g}{&#92;partial x_j}, &#92;mathcal{F}&#92;lambda &#92;rangle = &#92;langle g, &#92;frac{&#92;partial}{&#92;partial x_j} (&#92;mathcal{F}&#92;lambda) &#92;rangle &#92;end{array} ' title='&#92;displaystyle  &#92;begin{array}{rcl}  &#92;langle g, &#92;mathcal{F}(-2&#92;pi i x_j &#92;lambda) &#92;rangle &amp;= &#92;langle &#92;mathcal{F}^*g, -2&#92;pi i x_j &#92;lambda &#92;rangle = &#92;langle 2&#92;pi i x_j &#92;mathcal{F}^*g, &#92;lambda &#92;rangle &#92;&#92; &amp; = - &#92;langle -2&#92;pi i x_j &#92;mathcal{F}^*g, &#92;lambda &#92;rangle = - &#92;langle &#92;mathcal{F}^*(&#92;frac{&#92;partial g}{&#92;partial x_j}), &#92;lambda &#92;rangle &#92;&#92; &amp; = - &#92;langle &#92;frac{&#92;partial g}{&#92;partial x_j}, &#92;mathcal{F}&#92;lambda &#92;rangle = &#92;langle g, &#92;frac{&#92;partial}{&#92;partial x_j} (&#92;mathcal{F}&#92;lambda) &#92;rangle &#92;end{array} ' class='latex' /></p>
<p> Therefore, <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmathcal%7BF%7D%28-2%5Cpi+i+x_j+%5Clambda%29+%3D+%5Cfrac%7B%5Cpartial%7D%7B%5Cpartial+x_j%7D%5Cmathcal%7BF%7D%5Clambda%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mathcal{F}(-2&#92;pi i x_j &#92;lambda) = &#92;frac{&#92;partial}{&#92;partial x_j}&#92;mathcal{F}&#92;lambda}' title='{&#92;mathcal{F}(-2&#92;pi i x_j &#92;lambda) = &#92;frac{&#92;partial}{&#92;partial x_j}&#92;mathcal{F}&#92;lambda}' class='latex' />.</p>
<p>
I&#8217;ll try and continue to add to this solutions list. I make no claims of accuracy, and any and all helpful comments are welcome. </p>
<br />  <a rel="nofollow" href="http://feeds.wordpress.com/1.0/gocomments/maxbaroi.wordpress.com/103/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/comments/maxbaroi.wordpress.com/103/" /></a> <a rel="nofollow" href="http://feeds.wordpress.com/1.0/godelicious/maxbaroi.wordpress.com/103/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/delicious/maxbaroi.wordpress.com/103/" /></a> <a rel="nofollow" href="http://feeds.wordpress.com/1.0/gofacebook/maxbaroi.wordpress.com/103/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/facebook/maxbaroi.wordpress.com/103/" /></a> <a rel="nofollow" href="http://feeds.wordpress.com/1.0/gotwitter/maxbaroi.wordpress.com/103/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/twitter/maxbaroi.wordpress.com/103/" /></a> <a rel="nofollow" href="http://feeds.wordpress.com/1.0/gostumble/maxbaroi.wordpress.com/103/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/stumble/maxbaroi.wordpress.com/103/" /></a> <a rel="nofollow" href="http://feeds.wordpress.com/1.0/godigg/maxbaroi.wordpress.com/103/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/digg/maxbaroi.wordpress.com/103/" /></a> <a rel="nofollow" href="http://feeds.wordpress.com/1.0/goreddit/maxbaroi.wordpress.com/103/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/reddit/maxbaroi.wordpress.com/103/" /></a> <img alt="" border="0" src="http://stats.wordpress.com/b.gif?host=maxbaroi.wordpress.com&amp;blog=6922221&amp;post=103&amp;subd=maxbaroi&amp;ref=&amp;feed=1" width="1" height="1" />]]></content:encoded>
			<wfw:commentRss>http://maxbaroi.wordpress.com/2009/05/19/solutions-to-selected-exercises-from-245c-notes-3-distributions/feed/</wfw:commentRss>
		<slash:comments>5</slash:comments>
	
		<media:content url="http://0.gravatar.com/avatar/40e1819f1064072b650dfcaca1d604f6?s=96&#38;d=identicon&#38;r=G" medium="image">
			<media:title type="html">maxbaroi</media:title>
		</media:content>
	</item>
		<item>
		<title>Solutions Notice for Notes 13</title>
		<link>http://maxbaroi.wordpress.com/2009/04/05/solutions-notes-for-notes-13/</link>
		<comments>http://maxbaroi.wordpress.com/2009/04/05/solutions-notes-for-notes-13/#comments</comments>
		<pubDate>Sun, 05 Apr 2009 00:13:44 +0000</pubDate>
		<dc:creator>maxbaroi</dc:creator>
				<category><![CDATA[Solutions Notice]]></category>

		<guid isPermaLink="false">http://maxbaroi.wordpress.com/?p=91</guid>
		<description><![CDATA[I have Notes 13 up and nearly completed. There&#8217;s one small fragment of Exercise 2 that needs to be done, and two parts to number 4 that need to be done. I found out that doing all the exercises a very time consuming task, and this is a significant lowering of the bar, but I&#8217;ll [...]<img alt="" border="0" src="http://stats.wordpress.com/b.gif?host=maxbaroi.wordpress.com&amp;blog=6922221&amp;post=91&amp;subd=maxbaroi&amp;ref=&amp;feed=1" width="1" height="1" />]]></description>
			<content:encoded><![CDATA[<p>I have Notes 13 up and nearly completed. There&#8217;s one small fragment of Exercise 2 that needs to be done, and two parts to number 4 that need to be done.</p>
<p>I found out that doing all the exercises a very time consuming task, and this is a significant lowering of the bar, but I&#8217;ll proably have to resign to just giving partial solutions or outlines for most exercises.</p>
<br />  <a rel="nofollow" href="http://feeds.wordpress.com/1.0/gocomments/maxbaroi.wordpress.com/91/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/comments/maxbaroi.wordpress.com/91/" /></a> <a rel="nofollow" href="http://feeds.wordpress.com/1.0/godelicious/maxbaroi.wordpress.com/91/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/delicious/maxbaroi.wordpress.com/91/" /></a> <a rel="nofollow" href="http://feeds.wordpress.com/1.0/gofacebook/maxbaroi.wordpress.com/91/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/facebook/maxbaroi.wordpress.com/91/" /></a> <a rel="nofollow" href="http://feeds.wordpress.com/1.0/gotwitter/maxbaroi.wordpress.com/91/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/twitter/maxbaroi.wordpress.com/91/" /></a> <a rel="nofollow" href="http://feeds.wordpress.com/1.0/gostumble/maxbaroi.wordpress.com/91/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/stumble/maxbaroi.wordpress.com/91/" /></a> <a rel="nofollow" href="http://feeds.wordpress.com/1.0/godigg/maxbaroi.wordpress.com/91/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/digg/maxbaroi.wordpress.com/91/" /></a> <a rel="nofollow" href="http://feeds.wordpress.com/1.0/goreddit/maxbaroi.wordpress.com/91/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/reddit/maxbaroi.wordpress.com/91/" /></a> <img alt="" border="0" src="http://stats.wordpress.com/b.gif?host=maxbaroi.wordpress.com&amp;blog=6922221&amp;post=91&amp;subd=maxbaroi&amp;ref=&amp;feed=1" width="1" height="1" />]]></content:encoded>
			<wfw:commentRss>http://maxbaroi.wordpress.com/2009/04/05/solutions-notes-for-notes-13/feed/</wfw:commentRss>
		<slash:comments>0</slash:comments>
	
		<media:content url="http://0.gravatar.com/avatar/40e1819f1064072b650dfcaca1d604f6?s=96&#38;d=identicon&#38;r=G" medium="image">
			<media:title type="html">maxbaroi</media:title>
		</media:content>
	</item>
		<item>
		<title>245B, Notes 13: Compactification and Metrisation</title>
		<link>http://maxbaroi.wordpress.com/2009/04/05/245b-notes-13-compactification-and-metrisation/</link>
		<comments>http://maxbaroi.wordpress.com/2009/04/05/245b-notes-13-compactification-and-metrisation/#comments</comments>
		<pubDate>Sun, 05 Apr 2009 00:06:40 +0000</pubDate>
		<dc:creator>maxbaroi</dc:creator>
				<category><![CDATA[245B]]></category>

		<guid isPermaLink="false">http://maxbaroi.wordpress.com/?p=84</guid>
		<description><![CDATA[Here are some partial solutions to the problems formulated in Notes 13 that can be found here. Exercise 1 Let be a locally compact Hausdorff space that isn&#8217;t compact. Let be the collection of subsets of such that if and only if is an open subset of or is a compact subset of . The [...]<img alt="" border="0" src="http://stats.wordpress.com/b.gif?host=maxbaroi.wordpress.com&amp;blog=6922221&amp;post=84&amp;subd=maxbaroi&amp;ref=&amp;feed=1" width="1" height="1" />]]></description>
			<content:encoded><![CDATA[<p>Here are some partial solutions to the problems formulated in Notes 13 that can be found <a href="http://terrytao.wordpress.com/2009/03/18/245b-notes-13-compactification-and-metrisation-optional/" target="_blank">here</a>.</p>
<p><span id="more-84"></span></p>
<p><strong> Exercise 1 </strong></p>
<p>Let <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> be a locally compact Hausdorff space that isn&#8217;t compact. Let <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmathcal%7BF%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mathcal{F}}' title='{&#92;mathcal{F}}' class='latex' /> be the collection of subsets of <img src='http://s0.wp.com/latex.php?latex=%7BX+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X &#92;cup &#92;{&#92;infty&#92;}}' title='{X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' /> such that <img src='http://s0.wp.com/latex.php?latex=%7BU+%5Cin+%5Cmathcal%7BF%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U &#92;in &#92;mathcal{F}}' title='{U &#92;in &#92;mathcal{F}}' class='latex' /> if and only if <img src='http://s0.wp.com/latex.php?latex=%7BU%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U}' title='{U}' class='latex' /> is an open subset of <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> or <img src='http://s0.wp.com/latex.php?latex=%7BU%5Ec%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U^c}' title='{U^c}' class='latex' /> is a compact subset of <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />. The empty-set is an open subset of <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> and therefore in <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmathcal%7BF%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mathcal{F}}' title='{&#92;mathcal{F}}' class='latex' />. It is also a compact subset of <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> and therefore <img src='http://s0.wp.com/latex.php?latex=%7BX+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X &#92;cup &#92;{&#92;infty&#92;}}' title='{X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' /> is in <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmathcal%7BF%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mathcal{F}}' title='{&#92;mathcal{F}}' class='latex' />.</p>
<p>Pick two sets <img src='http://s0.wp.com/latex.php?latex=%7BU%2CV+%5Cin+%5Cmathcal%7BF%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U,V &#92;in &#92;mathcal{F}}' title='{U,V &#92;in &#92;mathcal{F}}' class='latex' />. If both are open relative to <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />, then <img src='http://s0.wp.com/latex.php?latex=%7BU+%5Ccap+V%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U &#92;cap V}' title='{U &#92;cap V}' class='latex' /> is open relative to <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> and thus lies in <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmathcal%7BF%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mathcal{F}}' title='{&#92;mathcal{F}}' class='latex' />. If both <img src='http://s0.wp.com/latex.php?latex=%7BU%5Ec%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U^c}' title='{U^c}' class='latex' /> and <img src='http://s0.wp.com/latex.php?latex=%7BV%5Ec%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{V^c}' title='{V^c}' class='latex' /> are compact subsets of <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />, then so is <img src='http://s0.wp.com/latex.php?latex=%7BU%5Ec+%5Ccup+V%5Ec%3D+%7B%28U+%5Ccap+V%29%7D%5Ec%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U^c &#92;cup V^c= {(U &#92;cap V)}^c}' title='{U^c &#92;cup V^c= {(U &#92;cap V)}^c}' class='latex' />, and therefore <img src='http://s0.wp.com/latex.php?latex=%7BU+%5Ccap+V%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U &#92;cap V}' title='{U &#92;cap V}' class='latex' /> is in <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmathcal%7BF%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mathcal{F}}' title='{&#92;mathcal{F}}' class='latex' />. If <img src='http://s0.wp.com/latex.php?latex=%7BU%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U}' title='{U}' class='latex' /> is an open set of <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />, and <img src='http://s0.wp.com/latex.php?latex=%7BV%5Ec%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{V^c}' title='{V^c}' class='latex' /> is a compact subset of <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />. Then <img src='http://s0.wp.com/latex.php?latex=%7BU+%5Ccap+V+%3D+U+%5Ccap+%28X+%5Cbackslash+V%5Ec%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U &#92;cap V = U &#92;cap (X &#92;backslash V^c)}' title='{U &#92;cap V = U &#92;cap (X &#92;backslash V^c)}' class='latex' /> since <img src='http://s0.wp.com/latex.php?latex=%7BV+%3D+%28X+%5Cbackslash+V%5Ec%29+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{V = (X &#92;backslash V^c) &#92;cup &#92;{&#92;infty&#92;}}' title='{V = (X &#92;backslash V^c) &#92;cup &#92;{&#92;infty&#92;}}' class='latex' /> and <img src='http://s0.wp.com/latex.php?latex=%7BU%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U}' title='{U}' class='latex' /> does not contain <img src='http://s0.wp.com/latex.php?latex=%7B%5Cinfty%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;infty}' title='{&#92;infty}' class='latex' />. Well, <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> is Hausdorff and therefore <img src='http://s0.wp.com/latex.php?latex=%7BV%5Ec%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{V^c}' title='{V^c}' class='latex' /> is closed relative to <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />, and thus <img src='http://s0.wp.com/latex.php?latex=%7B%28X+%5Cbackslash+V%5Ec%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{(X &#92;backslash V^c)}' title='{(X &#92;backslash V^c)}' class='latex' /> is open relative to <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7BU+%5Ccap+V%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U &#92;cap V}' title='{U &#92;cap V}' class='latex' /> must then be open relative to <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> and therefore lies in <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmathcal%7BF%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mathcal{F}}' title='{&#92;mathcal{F}}' class='latex' />.</p>
<p>Let <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7BU_%5Calpha%5C%7D_%7B%5Calpha+%5Cin+A%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{U_&#92;alpha&#92;}_{&#92;alpha &#92;in A}}' title='{&#92;{U_&#92;alpha&#92;}_{&#92;alpha &#92;in A}}' class='latex' /> be a collection of subsets of <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmathcal%7BF%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mathcal{F}}' title='{&#92;mathcal{F}}' class='latex' />. Then <img src='http://s0.wp.com/latex.php?latex=%7B%5Ccup_%7B%5Calpha+%5Cin+A%7D+U_%5Calpha+%3D+%28%5Ccup_%7B%5Calpha+%5Cin+B%7D+U_%5Calpha%29+%5Ccup+%28%5Ccup_%7B%5Calpha+%5Cin+C%7D+U_%5Calpha%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;cup_{&#92;alpha &#92;in A} U_&#92;alpha = (&#92;cup_{&#92;alpha &#92;in B} U_&#92;alpha) &#92;cup (&#92;cup_{&#92;alpha &#92;in C} U_&#92;alpha)}' title='{&#92;cup_{&#92;alpha &#92;in A} U_&#92;alpha = (&#92;cup_{&#92;alpha &#92;in B} U_&#92;alpha) &#92;cup (&#92;cup_{&#92;alpha &#92;in C} U_&#92;alpha)}' class='latex' /> where <img src='http://s0.wp.com/latex.php?latex=%7B%5Calpha+%5Cin+B%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;alpha &#92;in B}' title='{&#92;alpha &#92;in B}' class='latex' /> if <img src='http://s0.wp.com/latex.php?latex=%7BU_%5Calpha%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U_&#92;alpha}' title='{U_&#92;alpha}' class='latex' /> is open relative to <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />, and <img src='http://s0.wp.com/latex.php?latex=%7B%5Calpha+%5Cin+C%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;alpha &#92;in C}' title='{&#92;alpha &#92;in C}' class='latex' /> if <img src='http://s0.wp.com/latex.php?latex=%7BU_%5Calpha%5Ec%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U_&#92;alpha^c}' title='{U_&#92;alpha^c}' class='latex' /> is a compact subset of <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />. Let <img src='http://s0.wp.com/latex.php?latex=%7BV+%3D+%5Ccup_%7B%5Calpha+%5Cin+B%7D+U_%5Calpha%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{V = &#92;cup_{&#92;alpha &#92;in B} U_&#92;alpha}' title='{V = &#92;cup_{&#92;alpha &#92;in B} U_&#92;alpha}' class='latex' />, then <img src='http://s0.wp.com/latex.php?latex=%7BV%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{V}' title='{V}' class='latex' /> is an open subset of <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />. Let <img src='http://s0.wp.com/latex.php?latex=%7BW+%3D+%5Ccup_%7B%5Calpha+%5Cin+C%7D+U_%5Calpha%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{W = &#92;cup_{&#92;alpha &#92;in C} U_&#92;alpha}' title='{W = &#92;cup_{&#92;alpha &#92;in C} U_&#92;alpha}' class='latex' />, then <img src='http://s0.wp.com/latex.php?latex=%7BW%5Ec+%3D+%5Ccap_%7B%5Calpha+%5Cin+C%7D+U_%5Calpha%5Ec%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{W^c = &#92;cap_{&#92;alpha &#92;in C} U_&#92;alpha^c}' title='{W^c = &#92;cap_{&#92;alpha &#92;in C} U_&#92;alpha^c}' class='latex' />. Each <img src='http://s0.wp.com/latex.php?latex=%7BU_%5Calpha%5Ec%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U_&#92;alpha^c}' title='{U_&#92;alpha^c}' class='latex' /> is closed relative to <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> since the space is Hausdorff. Thus <img src='http://s0.wp.com/latex.php?latex=%7BW%5Ec%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{W^c}' title='{W^c}' class='latex' /> is closed, and is a subset of a compact set, and therefore compact. So we know that <img src='http://s0.wp.com/latex.php?latex=%7BV%2CW%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{V,W}' title='{V,W}' class='latex' /> lie in <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmathcal%7BF%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mathcal{F}}' title='{&#92;mathcal{F}}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7BV%5Ec+%5Ccap+W%5Ec+%3D+%28X+%5Cbackslash+V%29+%5Ccap+W%5Ec%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{V^c &#92;cap W^c = (X &#92;backslash V) &#92;cap W^c}' title='{V^c &#92;cap W^c = (X &#92;backslash V) &#92;cap W^c}' class='latex' /> since <img src='http://s0.wp.com/latex.php?latex=%7BW%5Ec%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{W^c}' title='{W^c}' class='latex' /> does not contain <img src='http://s0.wp.com/latex.php?latex=%7B%5Cinfty%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;infty}' title='{&#92;infty}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7BX+%5Cbackslash+V%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X &#92;backslash V}' title='{X &#92;backslash V}' class='latex' /> is a closed subset of <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />, and therefore <img src='http://s0.wp.com/latex.php?latex=%7BV%5Ec+%5Ccap+W%5Ec%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{V^c &#92;cap W^c}' title='{V^c &#92;cap W^c}' class='latex' /> is a closed subset of the compact subset <img src='http://s0.wp.com/latex.php?latex=%7BW%5Ec%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{W^c}' title='{W^c}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7BV%5Ec+%5Ccap+W%5Ec%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{V^c &#92;cap W^c}' title='{V^c &#92;cap W^c}' class='latex' /> is a compact subset of <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />, and therefore <img src='http://s0.wp.com/latex.php?latex=%7BV+%5Ccup+W%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{V &#92;cup W}' title='{V &#92;cup W}' class='latex' /> is in <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmathcal%7BF%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mathcal{F}}' title='{&#92;mathcal{F}}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmathcal%7BF%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mathcal{F}}' title='{&#92;mathcal{F}}' class='latex' /> contains the empty-set and <img src='http://s0.wp.com/latex.php?latex=%7BX+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X &#92;cup &#92;{&#92;infty&#92;}}' title='{X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' />, it is closed under countable intersections and arbitrary unions. <img src='http://s0.wp.com/latex.php?latex=%7B%5Cmathcal%7BF%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;mathcal{F}}' title='{&#92;mathcal{F}}' class='latex' /> is a topology on <img src='http://s0.wp.com/latex.php?latex=%7BX+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X &#92;cup &#92;{&#92;infty&#92;}}' title='{X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' />.</p>
<p>Consider the map <img src='http://s0.wp.com/latex.php?latex=%7Bj%3A+X+%5Crightarrow+X+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{j: X &#92;rightarrow X &#92;cup &#92;{&#92;infty&#92;}}' title='{j: X &#92;rightarrow X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' /> where <img src='http://s0.wp.com/latex.php?latex=%7Bj%28x%29%3Dx%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{j(x)=x}' title='{j(x)=x}' class='latex' /> for all <img src='http://s0.wp.com/latex.php?latex=%7Bx+%5Cin+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x &#92;in X}' title='{x &#92;in X}' class='latex' />. Let <img src='http://s0.wp.com/latex.php?latex=%7BU+%5Csubset+X+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U &#92;subset X &#92;cup &#92;{&#92;infty&#92;}}' title='{U &#92;subset X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' /> be open in <img src='http://s0.wp.com/latex.php?latex=%7BX+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X &#92;cup &#92;{&#92;infty&#92;}}' title='{X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' />. Suppose <img src='http://s0.wp.com/latex.php?latex=%7BU%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U}' title='{U}' class='latex' /> is an open subset of <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />, then <img src='http://s0.wp.com/latex.php?latex=%7BU%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U}' title='{U}' class='latex' /> is open relative to <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> in the subspace topology inherited from <img src='http://s0.wp.com/latex.php?latex=%7BX+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X &#92;cup &#92;{&#92;infty&#92;}}' title='{X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7Bj%5E%7B-1%7D%28U%29%3DU%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{j^{-1}(U)=U}' title='{j^{-1}(U)=U}' class='latex' />, and is open. Now suppose that <img src='http://s0.wp.com/latex.php?latex=%7BU%5Ec%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U^c}' title='{U^c}' class='latex' /> is a compact subset of <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />. Then <img src='http://s0.wp.com/latex.php?latex=%7BU+%5Ccap+X+%3D+U+%5Cbackslash+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U &#92;cap X = U &#92;backslash &#92;{&#92;infty&#92;}}' title='{U &#92;cap X = U &#92;backslash &#92;{&#92;infty&#92;}}' class='latex' /> is an open set relative to <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> as a subspace of <img src='http://s0.wp.com/latex.php?latex=%7BX+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X &#92;cup &#92;{&#92;infty&#92;}}' title='{X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' />. Then <img src='http://s0.wp.com/latex.php?latex=%7Bj%5E%7B-1%7D%28X+%5Cbackslash+%28U+%5Cbackslash+%5C%7B%5Cinfty%5C%7D%29%29%3Dj%5E%7B-1%7D%28U%5Ec%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{j^{-1}(X &#92;backslash (U &#92;backslash &#92;{&#92;infty&#92;}))=j^{-1}(U^c)}' title='{j^{-1}(X &#92;backslash (U &#92;backslash &#92;{&#92;infty&#92;}))=j^{-1}(U^c)}' class='latex' /> and is therefore closed, thus <img src='http://s0.wp.com/latex.php?latex=%7Bj%5E%7B-1%7D%28X+%5Ccap+U%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{j^{-1}(X &#92;cap U)}' title='{j^{-1}(X &#92;cap U)}' class='latex' />, is open. Since there are only two types of open sets in <img src='http://s0.wp.com/latex.php?latex=%7BX+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X &#92;cup &#92;{&#92;infty&#92;}}' title='{X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' />, there are only two types of open sets in <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> when considered as a subspace of <img src='http://s0.wp.com/latex.php?latex=%7BX+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X &#92;cup &#92;{&#92;infty&#92;}}' title='{X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' />, and for both types in <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />, the inverse image under <img src='http://s0.wp.com/latex.php?latex=%7Bj%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{j}' title='{j}' class='latex' /> is open. <img src='http://s0.wp.com/latex.php?latex=%7Bj%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{j}' title='{j}' class='latex' /> is continuous. Now suppose <img src='http://s0.wp.com/latex.php?latex=%7BU%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U}' title='{U}' class='latex' /> is open in <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />, then by construction, <img src='http://s0.wp.com/latex.php?latex=%7BU%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U}' title='{U}' class='latex' /> is open in <img src='http://s0.wp.com/latex.php?latex=%7BX+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X &#92;cup &#92;{&#92;infty&#92;}}' title='{X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' />, and <img src='http://s0.wp.com/latex.php?latex=%7Bj%28U%29%3DU%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{j(U)=U}' title='{j(U)=U}' class='latex' />, so <img src='http://s0.wp.com/latex.php?latex=%7Bj%5E%7B-1%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{j^{-1}}' title='{j^{-1}}' class='latex' /> is continuous. <img src='http://s0.wp.com/latex.php?latex=%7Bj%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{j}' title='{j}' class='latex' /> is an embedding.</p>
<p><img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> is an open subset of <img src='http://s0.wp.com/latex.php?latex=%7BX+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X &#92;cup &#92;{&#92;infty&#92;}}' title='{X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' />. Now here&#8217;s where we use that <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> isn&#8217;t compact. Suppose that <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{&#92;infty&#92;}}' title='{&#92;{&#92;infty&#92;}}' class='latex' /> is an open set in <img src='http://s0.wp.com/latex.php?latex=%7BX+%5Ccup+%5Cinfty%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X &#92;cup &#92;infty}' title='{X &#92;cup &#92;infty}' class='latex' />, then since <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{&#92;infty&#92;}}' title='{&#92;{&#92;infty&#92;}}' class='latex' /> isn&#8217;t an open subset of <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />, the complement of <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{&#92;infty&#92;}}' title='{&#92;{&#92;infty&#92;}}' class='latex' /> is a compact subset of <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />, but the complement of <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{&#92;infty&#92;}}' title='{&#92;{&#92;infty&#92;}}' class='latex' /> is <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />, and by assumption, <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> isn&#8217;t compact. Therefore every open set containing <img src='http://s0.wp.com/latex.php?latex=%7B%5Cinfty%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;infty}' title='{&#92;infty}' class='latex' /> contains a point in it that isn&#8217;t <img src='http://s0.wp.com/latex.php?latex=%7B%5Cinfty%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;infty}' title='{&#92;infty}' class='latex' />, that said point must lie in <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7B%5Cinfty%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;infty}' title='{&#92;infty}' class='latex' /> is a limit point of <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />, as is every point in <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> is a dense open subset of <img src='http://s0.wp.com/latex.php?latex=%7BX+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X &#92;cup &#92;{&#92;infty&#92;}}' title='{X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' />. If <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> is compact, then when we consider <img src='http://s0.wp.com/latex.php?latex=%7BX+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X &#92;cup &#92;{&#92;infty&#92;}}' title='{X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' />, <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{&#92;infty&#92;}}' title='{&#92;{&#92;infty&#92;}}' class='latex' /> is an open neighborhood around <img src='http://s0.wp.com/latex.php?latex=%7B%5Cinfty%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;infty}' title='{&#92;infty}' class='latex' />, and therefore <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> isn&#8217;t dense in <img src='http://s0.wp.com/latex.php?latex=%7BX+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X &#92;cup &#92;{&#92;infty&#92;}}' title='{X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' />. The one point compactification process fails if <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> is compact.</p>
<p>We&#8217;re almost there, we just need to show that <img src='http://s0.wp.com/latex.php?latex=%7BX+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X &#92;cup &#92;{&#92;infty&#92;}}' title='{X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' /> is Hausdorff and compact. We already know we can separate any two point in <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> with disjoint open sets because any set that&#8217;s open in <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> is open in <img src='http://s0.wp.com/latex.php?latex=%7BX+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X &#92;cup &#92;{&#92;infty&#92;}}' title='{X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' />. Pick some <img src='http://s0.wp.com/latex.php?latex=%7Bx+%5Cin+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x &#92;in X}' title='{x &#92;in X}' class='latex' />. Since <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> is locally compact, there exists a compact set <img src='http://s0.wp.com/latex.php?latex=%7BF%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{F}' title='{F}' class='latex' /> such that <img src='http://s0.wp.com/latex.php?latex=%7Bx+%5Cin+F%5Eo%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x &#92;in F^o}' title='{x &#92;in F^o}' class='latex' />. Then the complement of <img src='http://s0.wp.com/latex.php?latex=%7BF%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{F}' title='{F}' class='latex' /> in <img src='http://s0.wp.com/latex.php?latex=%7BX+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X &#92;cup &#92;{&#92;infty&#92;}}' title='{X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' />, <img src='http://s0.wp.com/latex.php?latex=%7BF%5Ec%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{F^c}' title='{F^c}' class='latex' />, is an open set in <img src='http://s0.wp.com/latex.php?latex=%7BX+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X &#92;cup &#92;{&#92;infty&#92;}}' title='{X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' /> that contains <img src='http://s0.wp.com/latex.php?latex=%7B%5Cinfty%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;infty}' title='{&#92;infty}' class='latex' />, and <img src='http://s0.wp.com/latex.php?latex=%7BF%5Ec+%5Ccap+F%5Eo%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{F^c &#92;cap F^o}' title='{F^c &#92;cap F^o}' class='latex' /> is empty. We were able to separate <img src='http://s0.wp.com/latex.php?latex=%7B%5Cinfty%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;infty}' title='{&#92;infty}' class='latex' /> and any point in <img src='http://s0.wp.com/latex.php?latex=%7Bx%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x}' title='{x}' class='latex' /> by disjoint open sets. <img src='http://s0.wp.com/latex.php?latex=%7BX+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X &#92;cup &#92;{&#92;infty&#92;}}' title='{X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' /> is Hausdorff. Now let <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7BU_%5Calpha%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{U_&#92;alpha&#92;}}' title='{&#92;{U_&#92;alpha&#92;}}' class='latex' /> be an open cover in <img src='http://s0.wp.com/latex.php?latex=%7BX+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X &#92;cup &#92;{&#92;infty&#92;}}' title='{X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7B%5Cinfty%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;infty}' title='{&#92;infty}' class='latex' /> lies in some <img src='http://s0.wp.com/latex.php?latex=%7BU_%5Cbeta%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U_&#92;beta}' title='{U_&#92;beta}' class='latex' />. Remove <img src='http://s0.wp.com/latex.php?latex=%7BU_%5Cbeta%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U_&#92;beta}' title='{U_&#92;beta}' class='latex' /> from our collection of open sets, and let <img src='http://s0.wp.com/latex.php?latex=%7BK+%3D+U_%5Calpha%5Ec%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{K = U_&#92;alpha^c}' title='{K = U_&#92;alpha^c}' class='latex' />. Then our modified collection <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7BU_%5Calpha%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{U_&#92;alpha&#92;}}' title='{&#92;{U_&#92;alpha&#92;}}' class='latex' /> is an open cover of the <img src='http://s0.wp.com/latex.php?latex=%7BK%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{K}' title='{K}' class='latex' />. Now <img src='http://s0.wp.com/latex.php?latex=%7BK%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{K}' title='{K}' class='latex' /> is a compact subset of <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />. consider the collection of sets <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7BV_%5Calpha%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{V_&#92;alpha&#92;}}' title='{&#92;{V_&#92;alpha&#92;}}' class='latex' /> where each <img src='http://s0.wp.com/latex.php?latex=%7BV_%5Calpha%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{V_&#92;alpha}' title='{V_&#92;alpha}' class='latex' /> is equal to <img src='http://s0.wp.com/latex.php?latex=%7BX+%5Ccap+U_%5Calpha%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X &#92;cap U_&#92;alpha}' title='{X &#92;cap U_&#92;alpha}' class='latex' />. We&#8217;ve already shown in this proof that each <img src='http://s0.wp.com/latex.php?latex=%7BV_%5Calpha%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{V_&#92;alpha}' title='{V_&#92;alpha}' class='latex' /> is open in <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />. Therefore the <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7BV_%5Calpha%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{V_&#92;alpha&#92;}}' title='{&#92;{V_&#92;alpha&#92;}}' class='latex' /> is an open cover of the compact set <img src='http://s0.wp.com/latex.php?latex=%7BK%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{K}' title='{K}' class='latex' />. There exists a finite sub-cover <img src='http://s0.wp.com/latex.php?latex=%7BV_%7B%5Calpha_1%7D%2C%5Cldots%2CV_%7B%5Calpha_n%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{V_{&#92;alpha_1},&#92;ldots,V_{&#92;alpha_n}}' title='{V_{&#92;alpha_1},&#92;ldots,V_{&#92;alpha_n}}' class='latex' />. Then <img src='http://s0.wp.com/latex.php?latex=%7BU_%5Cbeta%2CU_%7B%5Calpha_1%7D%2C%5Cldots%2CU_%7B%5Calpha_n%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U_&#92;beta,U_{&#92;alpha_1},&#92;ldots,U_{&#92;alpha_n}}' title='{U_&#92;beta,U_{&#92;alpha_1},&#92;ldots,U_{&#92;alpha_n}}' class='latex' /> is a finite sub-cover of <img src='http://s0.wp.com/latex.php?latex=%7BX+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X &#92;cup &#92;{&#92;infty&#92;}}' title='{X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' />. Every open cover of <img src='http://s0.wp.com/latex.php?latex=%7BX+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X &#92;cup &#92;{&#92;infty&#92;}}' title='{X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' /> gives arise to a finite sub-cover. <img src='http://s0.wp.com/latex.php?latex=%7BX+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X &#92;cup &#92;{&#92;infty&#92;}}' title='{X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' /> is compact.</p>
<p>We&#8217;ve shown an embedding <img src='http://s0.wp.com/latex.php?latex=%7Bj%3A+X+%5Crightarrow+X+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{j: X &#92;rightarrow X &#92;cup &#92;{&#92;infty&#92;}}' title='{j: X &#92;rightarrow X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' /> where <img src='http://s0.wp.com/latex.php?latex=%7BX+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X &#92;cup &#92;{&#92;infty&#92;}}' title='{X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' /> is a compact Hausdorff space that has <img src='http://s0.wp.com/latex.php?latex=%7Bj%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{j(X)}' title='{j(X)}' class='latex' /> as a dense open sub-set. <img src='http://s0.wp.com/latex.php?latex=%7Bj%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{j}' title='{j}' class='latex' /> is a compactification.</p>
<p>Let <img src='http://s0.wp.com/latex.php?latex=%7Bi%3AX+%5Crightarrow+%5Coverline%7BX%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i:X &#92;rightarrow &#92;overline{X}}' title='{i:X &#92;rightarrow &#92;overline{X}}' class='latex' /> be some compactification, and let <img src='http://s0.wp.com/latex.php?latex=%7Bj%3AX+%5Crightarrow+X+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{j:X &#92;rightarrow X &#92;cup &#92;{&#92;infty&#92;}}' title='{j:X &#92;rightarrow X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' /> be the one-point compactification. We want to show that <img src='http://s0.wp.com/latex.php?latex=%7Bi%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i}' title='{i}' class='latex' /> is finer than <img src='http://s0.wp.com/latex.php?latex=%7Bj%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{j}' title='{j}' class='latex' />. We need to find a continuous map <img src='http://s0.wp.com/latex.php?latex=%7B%5Cpi%3A%5Coverline%7BX%7D+%5Crightarrow+X+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;pi:&#92;overline{X} &#92;rightarrow X &#92;cup &#92;{&#92;infty&#92;}}' title='{&#92;pi:&#92;overline{X} &#92;rightarrow X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' /> such that <img src='http://s0.wp.com/latex.php?latex=%7Bj+%3D+%5Cpi+%5Ccirc+i%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{j = &#92;pi &#92;circ i}' title='{j = &#92;pi &#92;circ i}' class='latex' />. We&#8217;ll define <img src='http://s0.wp.com/latex.php?latex=%7B%5Cpi%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;pi}' title='{&#92;pi}' class='latex' /> as follows. If <img src='http://s0.wp.com/latex.php?latex=%7By+%5Cin+i%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{y &#92;in i(X)}' title='{y &#92;in i(X)}' class='latex' />, then let <img src='http://s0.wp.com/latex.php?latex=%7B%5Cpi%28y%29%3Dx%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;pi(y)=x}' title='{&#92;pi(y)=x}' class='latex' /> where <img src='http://s0.wp.com/latex.php?latex=%7Bx%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x}' title='{x}' class='latex' /> is the element in <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> such that <img src='http://s0.wp.com/latex.php?latex=%7By+%3D+i%28x%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{y = i(x)}' title='{y = i(x)}' class='latex' />. And if <img src='http://s0.wp.com/latex.php?latex=%7By%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{y}' title='{y}' class='latex' /> is not in <img src='http://s0.wp.com/latex.php?latex=%7Bi%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i(X)}' title='{i(X)}' class='latex' />, let <img src='http://s0.wp.com/latex.php?latex=%7B%5Cpi%28y%29%3D%5Cinfty%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;pi(y)=&#92;infty}' title='{&#92;pi(y)=&#92;infty}' class='latex' />. Then <img src='http://s0.wp.com/latex.php?latex=%7Bj+%3D+%5Cpi+%5Ccirc+i%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{j = &#92;pi &#92;circ i}' title='{j = &#92;pi &#92;circ i}' class='latex' />.</p>
<p>Now to show that it is continuous. Let <img src='http://s0.wp.com/latex.php?latex=%7BU%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U}' title='{U}' class='latex' /> be an open set in <img src='http://s0.wp.com/latex.php?latex=%7BX+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X &#92;cup &#92;{&#92;infty&#92;}}' title='{X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' />. Suppose <img src='http://s0.wp.com/latex.php?latex=%7B%5Cinfty%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;infty}' title='{&#92;infty}' class='latex' /> is not in <img src='http://s0.wp.com/latex.php?latex=%7BU%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U}' title='{U}' class='latex' />. Then <img src='http://s0.wp.com/latex.php?latex=%7B%5Cpi%5E%7B-1%7D%28U%29+%3D+i%28U%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;pi^{-1}(U) = i(U)}' title='{&#92;pi^{-1}(U) = i(U)}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7BU+%5Csubset+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U &#92;subset X}' title='{U &#92;subset X}' class='latex' />, and is therefore open relative to <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7Bi%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i}' title='{i}' class='latex' /> is a homeomorphism between <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> and <img src='http://s0.wp.com/latex.php?latex=%7Bi%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i(X)}' title='{i(X)}' class='latex' />, and thus <img src='http://s0.wp.com/latex.php?latex=%7Bi%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i}' title='{i}' class='latex' /> maps open sets to open sets. Therefore, <img src='http://s0.wp.com/latex.php?latex=%7B%5Cpi%5E%7B-1%7D%28U%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;pi^{-1}(U)}' title='{&#92;pi^{-1}(U)}' class='latex' /> is open relative to <img src='http://s0.wp.com/latex.php?latex=%7Bi%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i(X)}' title='{i(X)}' class='latex' />, and since <img src='http://s0.wp.com/latex.php?latex=%7Bi%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i(X)}' title='{i(X)}' class='latex' /> is open relative to <img src='http://s0.wp.com/latex.php?latex=%7B%5Coverline%7BX%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;overline{X}}' title='{&#92;overline{X}}' class='latex' />, <img src='http://s0.wp.com/latex.php?latex=%7B%5Cpi%5E%7B-1%7D%28U%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;pi^{-1}(U)}' title='{&#92;pi^{-1}(U)}' class='latex' /> is open in <img src='http://s0.wp.com/latex.php?latex=%7B%5Coverline%7BX%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;overline{X}}' title='{&#92;overline{X}}' class='latex' />. Now suppose <img src='http://s0.wp.com/latex.php?latex=%7B%5Cinfty+%5Cin+U%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;infty &#92;in U}' title='{&#92;infty &#92;in U}' class='latex' />. Now <img src='http://s0.wp.com/latex.php?latex=%7BF+%3D+U%5Ec%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{F = U^c}' title='{F = U^c}' class='latex' /> is closed in <img src='http://s0.wp.com/latex.php?latex=%7BX+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X &#92;cup &#92;{&#92;infty&#92;}}' title='{X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' />, and does not contain <img src='http://s0.wp.com/latex.php?latex=%7B%5Cinfty%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;infty}' title='{&#92;infty}' class='latex' />. By the definition of the one-point compactification of <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />, <img src='http://s0.wp.com/latex.php?latex=%7BF%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{F}' title='{F}' class='latex' /> is a compact subset of the space <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />. Now <img src='http://s0.wp.com/latex.php?latex=%7B%5Cpi%5E%7B-1%7D%28F%29%3Di%28F%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;pi^{-1}(F)=i(F)}' title='{&#92;pi^{-1}(F)=i(F)}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7Bi%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i}' title='{i}' class='latex' /> is continuous, and thus maps compact sets to compact sets. <img src='http://s0.wp.com/latex.php?latex=%7Bi%28F%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i(F)}' title='{i(F)}' class='latex' /> is a compact subset of the Hausdorff space <img src='http://s0.wp.com/latex.php?latex=%7B%5Coverline%7BX%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;overline{X}}' title='{&#92;overline{X}}' class='latex' />, and therefore closed. <img src='http://s0.wp.com/latex.php?latex=%7B%5Cpi%5E%7B-1%7D%28F%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;pi^{-1}(F)}' title='{&#92;pi^{-1}(F)}' class='latex' /> is closed. Therefore <img src='http://s0.wp.com/latex.php?latex=%7B%7B%5Cpi%5E%7B-1%7D%28F%29%7D%5Ec%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{{&#92;pi^{-1}(F)}^c}' title='{{&#92;pi^{-1}(F)}^c}' class='latex' /> is open, and that&#8217;s equal to <img src='http://s0.wp.com/latex.php?latex=%7B%5Cpi%5E%7B-1%7D%28F%5Ec%29%3D%5Cpi%5E%7B-1%7D%28U%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;pi^{-1}(F^c)=&#92;pi^{-1}(U)}' title='{&#92;pi^{-1}(F^c)=&#92;pi^{-1}(U)}' class='latex' />. We&#8217;ve exhausted our cases. <img src='http://s0.wp.com/latex.php?latex=%7B%5Cpi%5E%7B-1%7D%28U%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;pi^{-1}(U)}' title='{&#92;pi^{-1}(U)}' class='latex' /> is open whenever <img src='http://s0.wp.com/latex.php?latex=%7BU%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U}' title='{U}' class='latex' /> is open in <img src='http://s0.wp.com/latex.php?latex=%7BX+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X &#92;cup &#92;{&#92;infty&#92;}}' title='{X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' />. We have found our desired continuous function <img src='http://s0.wp.com/latex.php?latex=%7B%5Cpi%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;pi}' title='{&#92;pi}' class='latex' /> from <img src='http://s0.wp.com/latex.php?latex=%7B%5Coverline%7BX%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;overline{X}}' title='{&#92;overline{X}}' class='latex' /> to <img src='http://s0.wp.com/latex.php?latex=%7BX+%5Ccup+%5C%7B%5Cinfty%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X &#92;cup &#92;{&#92;infty&#92;}}' title='{X &#92;cup &#92;{&#92;infty&#92;}}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7Bj%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{j}' title='{j}' class='latex' /> is courser than <img src='http://s0.wp.com/latex.php?latex=%7Bi%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i}' title='{i}' class='latex' />, and since <img src='http://s0.wp.com/latex.php?latex=%7Bi%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i}' title='{i}' class='latex' /> was an arbitrary compactification, we see that the one-point compactification is courser than any other compactification.</p>
<p><strong> Exercise 2 </strong></p>
<p>Consider the continuous function <img src='http://s0.wp.com/latex.php?latex=%7Bf+%3A+X+%5Crightarrow+Y%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f : X &#92;rightarrow Y}' title='{f : X &#92;rightarrow Y}' class='latex' />, and suppose that there exists a continuous extension of <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' /> to a function <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+f%3A+%5Cbeta+X+%5Crightarrow+%5Cbeta+Y%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta f: &#92;beta X &#92;rightarrow &#92;beta Y}' title='{&#92;beta f: &#92;beta X &#92;rightarrow &#92;beta Y}' class='latex' />. Let <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+f%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta f}' title='{&#92;beta f}' class='latex' /> and <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+f%5E%5Cprime%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta f^&#92;prime}' title='{&#92;beta f^&#92;prime}' class='latex' /> from <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' /> to <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+Y%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta Y}' title='{&#92;beta Y}' class='latex' /> be continuous extensions of <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' />. Pick some <img src='http://s0.wp.com/latex.php?latex=%7Bx+%5Cin+%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x &#92;in &#92;beta X}' title='{x &#92;in &#92;beta X}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> can be considered an open dense subset of <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' />, so pick some net <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7Bx_%5Calpha%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{x_&#92;alpha&#92;}}' title='{&#92;{x_&#92;alpha&#92;}}' class='latex' /> in <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> that converges to <img src='http://s0.wp.com/latex.php?latex=%7Bx%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x}' title='{x}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' /> a continuous function on <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' />, and since <img src='http://s0.wp.com/latex.php?latex=%7Bx_%5Calpha+%5Crightarrow+x%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x_&#92;alpha &#92;rightarrow x}' title='{x_&#92;alpha &#92;rightarrow x}' class='latex' /> we have <img src='http://s0.wp.com/latex.php?latex=%7Bf%28x_%5Calpha%29+%5Crightarrow+f%28x%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f(x_&#92;alpha) &#92;rightarrow f(x)}' title='{f(x_&#92;alpha) &#92;rightarrow f(x)}' class='latex' />. Similarly, we have <img src='http://s0.wp.com/latex.php?latex=%7Bf%5E%5Cprime%28x_%5Calpha%29+%5Crightarrow+f%5E%5Cprime%28x%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f^&#92;prime(x_&#92;alpha) &#92;rightarrow f^&#92;prime(x)}' title='{f^&#92;prime(x_&#92;alpha) &#92;rightarrow f^&#92;prime(x)}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' /> and <img src='http://s0.wp.com/latex.php?latex=%7Bf%5E%5Cprime%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f^&#92;prime}' title='{f^&#92;prime}' class='latex' /> agree on <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />, and therefore we have the net <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7Bf%28x_%5Calpha%29%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{f(x_&#92;alpha)&#92;}}' title='{&#92;{f(x_&#92;alpha)&#92;}}' class='latex' /> converging to <img src='http://s0.wp.com/latex.php?latex=%7Bf%28x%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f(x)}' title='{f(x)}' class='latex' /> and <img src='http://s0.wp.com/latex.php?latex=%7Bf%5E%5Cprime%28x%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f^&#92;prime(x)}' title='{f^&#92;prime(x)}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+Y%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta Y}' title='{&#92;beta Y}' class='latex' /> is a Hausdorff space and thus every net converges to at most one point. So we see that <img src='http://s0.wp.com/latex.php?latex=%7Bf%28x%29%3Df%5E%5Cprime%28x%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f(x)=f^&#92;prime(x)}' title='{f(x)=f^&#92;prime(x)}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' /> and <img src='http://s0.wp.com/latex.php?latex=%7Bf%5E%5Cprime%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f^&#92;prime}' title='{f^&#92;prime}' class='latex' /> agree everywhere. If an extension of <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' /> exists, it is unique.</p>
<p>Now to show that an extension always exists. Consider the graph <img src='http://s0.wp.com/latex.php?latex=%7BE+%3D+%5C%7B%28x%2Cf%28x%29%29%3Ax+%5Cin+X%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{E = &#92;{(x,f(x)):x &#92;in X&#92;}}' title='{E = &#92;{(x,f(x)):x &#92;in X&#92;}}' class='latex' />. consider the closure of <img src='http://s0.wp.com/latex.php?latex=%7BE%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{E}' title='{E}' class='latex' /> in <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X+%5Ctimes+%5Cbeta+Y%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X &#92;times &#92;beta Y}' title='{&#92;beta X &#92;times &#92;beta Y}' class='latex' />. Note that <img src='http://s0.wp.com/latex.php?latex=%7BX+%5Ctimes+Y%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X &#92;times Y}' title='{X &#92;times Y}' class='latex' /> is a dense open set in <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X+%5Ctimes+%5Cbeta+Y%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X &#92;times &#92;beta Y}' title='{&#92;beta X &#92;times &#92;beta Y}' class='latex' />. Let <img src='http://s0.wp.com/latex.php?latex=%7B%28x%2Cy%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{(x,y)}' title='{(x,y)}' class='latex' /> be a limit point in <img src='http://s0.wp.com/latex.php?latex=%7BE%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{E}' title='{E}' class='latex' />, that is, there exists a net <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7B%28x_%5Calpha%2Cf%28x_%5Calpha%29%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{(x_&#92;alpha,f(x_&#92;alpha)&#92;}}' title='{&#92;{(x_&#92;alpha,f(x_&#92;alpha)&#92;}}' class='latex' /> that converges to <img src='http://s0.wp.com/latex.php?latex=%7B%28x%2Cy%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{(x,y)}' title='{(x,y)}' class='latex' />. Similarly, let <img src='http://s0.wp.com/latex.php?latex=%7B%28x%2Cz%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{(x,z)}' title='{(x,z)}' class='latex' /> be another limit point of <img src='http://s0.wp.com/latex.php?latex=%7BE%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{E}' title='{E}' class='latex' />, and let <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7B%28x_%5Cbeta%2Cf%28x_%5Cbeta%29%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{(x_&#92;beta,f(x_&#92;beta)&#92;}}' title='{&#92;{(x_&#92;beta,f(x_&#92;beta)&#92;}}' class='latex' /> be a net in <img src='http://s0.wp.com/latex.php?latex=%7BE%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{E}' title='{E}' class='latex' /> that converges to <img src='http://s0.wp.com/latex.php?latex=%7B%28x%2Cz%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{(x,z)}' title='{(x,z)}' class='latex' />. NEED TO SHOW THAT <img src='http://s0.wp.com/latex.php?latex=%7By%3Dz%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{y=z}' title='{y=z}' class='latex' /> AND THUS THE CLOSURE OF <img src='http://s0.wp.com/latex.php?latex=%7BE%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{E}' title='{E}' class='latex' /> IS A FUNCTION, AND THEN THAT <img src='http://s0.wp.com/latex.php?latex=%7BE%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{E}' title='{E}' class='latex' /> IS CONTINUOUS.</p>
<p>Now to show the converse. Let <img src='http://s0.wp.com/latex.php?latex=%7Bi%3AX+%5Crightarrow+%5Coverline%7BX%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i:X &#92;rightarrow &#92;overline{X}}' title='{i:X &#92;rightarrow &#92;overline{X}}' class='latex' /> be a compactification of <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> such that every continuous map <img src='http://s0.wp.com/latex.php?latex=%7Bf%3A+X+%5Crightarrow+K%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f: X &#92;rightarrow K}' title='{f: X &#92;rightarrow K}' class='latex' /> where <img src='http://s0.wp.com/latex.php?latex=%7BK%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{K}' title='{K}' class='latex' /> is compact can be extended continuously to <img src='http://s0.wp.com/latex.php?latex=%7B%5Coverline%7BX%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;overline{X}}' title='{&#92;overline{X}}' class='latex' />. We can identify <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> as a subspace of <img src='http://s0.wp.com/latex.php?latex=%7B%5Coverline%7BX%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;overline{X}}' title='{&#92;overline{X}}' class='latex' /> without loss of generality. Let <img src='http://s0.wp.com/latex.php?latex=%7Bj%3A+X+%5Crightarrow+%5Coverline%7BX%7D%5E%5Cprime%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{j: X &#92;rightarrow &#92;overline{X}^&#92;prime}' title='{j: X &#92;rightarrow &#92;overline{X}^&#92;prime}' class='latex' /> be any other compactification of <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />. We need to show that <img src='http://s0.wp.com/latex.php?latex=%7Bi%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i}' title='{i}' class='latex' /> finer than <img src='http://s0.wp.com/latex.php?latex=%7Bj%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{j}' title='{j}' class='latex' />, that is, that there exists a continuous function <img src='http://s0.wp.com/latex.php?latex=%7B%5Cpi+%3A+%5Coverline%7BX%7D+%5Crightarrow+%5Coverline%7BX%7D%5E%5Cprime%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;pi : &#92;overline{X} &#92;rightarrow &#92;overline{X}^&#92;prime}' title='{&#92;pi : &#92;overline{X} &#92;rightarrow &#92;overline{X}^&#92;prime}' class='latex' /> such that <img src='http://s0.wp.com/latex.php?latex=%7Bj+%3D+%5Cpi+%5Ccirc+i%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{j = &#92;pi &#92;circ i}' title='{j = &#92;pi &#92;circ i}' class='latex' />. Well, <img src='http://s0.wp.com/latex.php?latex=%7Bj%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{j}' title='{j}' class='latex' /> is a continuous map from <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> to a compact set, namely <img src='http://s0.wp.com/latex.php?latex=%7B%5Coverline%7BX%7D%5E%5Cprime%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;overline{X}^&#92;prime}' title='{&#92;overline{X}^&#92;prime}' class='latex' />, so there exists an continuous extension <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+j%3A+%5Coverline%7BX%7D+%5Crightarrow+%5Coverline%7BX%5E%5Cprime%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta j: &#92;overline{X} &#92;rightarrow &#92;overline{X^&#92;prime}}' title='{&#92;beta j: &#92;overline{X} &#92;rightarrow &#92;overline{X^&#92;prime}}' class='latex' />. Since we&#8217;re considering <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> to be a subset of <img src='http://s0.wp.com/latex.php?latex=%7B%5Coverline%7BX%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;overline{X}}' title='{&#92;overline{X}}' class='latex' />, <img src='http://s0.wp.com/latex.php?latex=%7Bi%28x%29%3Dx%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i(x)=x}' title='{i(x)=x}' class='latex' /> for all <img src='http://s0.wp.com/latex.php?latex=%7Bx+%5Cin+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x &#92;in X}' title='{x &#92;in X}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+j%7C_X+%3Dj%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta j|_X =j}' title='{&#92;beta j|_X =j}' class='latex' />, therefore <img src='http://s0.wp.com/latex.php?latex=%7Bj+%3D+%5Cbeta+j+%5Ccirc+i%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{j = &#92;beta j &#92;circ i}' title='{j = &#92;beta j &#92;circ i}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7Bi%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i}' title='{i}' class='latex' /> is finer than <img src='http://s0.wp.com/latex.php?latex=%7Bj%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{j}' title='{j}' class='latex' />, and since <img src='http://s0.wp.com/latex.php?latex=%7Bj%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{j}' title='{j}' class='latex' /> was arbitrary, that must mean that <img src='http://s0.wp.com/latex.php?latex=%7Bi%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i}' title='{i}' class='latex' /> is the Stone-Cech compactification.</p>
<p><strong> Exercise 3 </strong></p>
<p><strong> Bullet Point One </strong></p>
<p><img src='http://s0.wp.com/latex.php?latex=%7BQ%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{Q}' title='{Q}' class='latex' /> is the direct product of compact spaces with the product topology, and therefore compact by Tychonoff&#8217;s Theorem. <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' /> is a closed subset of <img src='http://s0.wp.com/latex.php?latex=%7BQ%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{Q}' title='{Q}' class='latex' /> and therefore compact, now we need to show that <img src='http://s0.wp.com/latex.php?latex=%7Bi%3AX+%5Crightarrow+%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i:X &#92;rightarrow &#92;beta X}' title='{i:X &#92;rightarrow &#92;beta X}' class='latex' /> is a compactification. We also need to note that since <img src='http://s0.wp.com/latex.php?latex=%7BQ%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{Q}' title='{Q}' class='latex' /> is the product of Hausdorff spaces, <img src='http://s0.wp.com/latex.php?latex=%7BQ%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{Q}' title='{Q}' class='latex' /> is Hausdorff and sine we know it&#8217;s compact, <img src='http://s0.wp.com/latex.php?latex=%7BQ%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{Q}' title='{Q}' class='latex' /> is normal. We need to show that <img src='http://s0.wp.com/latex.php?latex=%7Bi%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i}' title='{i}' class='latex' /> is a homeomorphism between <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> and <img src='http://s0.wp.com/latex.php?latex=%7Bi%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i(X)}' title='{i(X)}' class='latex' /> and that <img src='http://s0.wp.com/latex.php?latex=%7Bi%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i(X)}' title='{i(X)}' class='latex' /> is an open dense subset of <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' />.</p>
<p>First let&#8217;s show that <img src='http://s0.wp.com/latex.php?latex=%7Bi%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i}' title='{i}' class='latex' /> is injective, and therefore bijective between <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> and <img src='http://s0.wp.com/latex.php?latex=%7Bi%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i(X)}' title='{i(X)}' class='latex' />. Pick two points <img src='http://s0.wp.com/latex.php?latex=%7Bx%2Cy+%5Cin+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x,y &#92;in X}' title='{x,y &#92;in X}' class='latex' /> that aren&#8217;t equal. <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> is Hausdorff and therefore <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7Bx%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{x&#92;}}' title='{&#92;{x&#92;}}' class='latex' /> and <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7By%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{y&#92;}}' title='{&#92;{y&#92;}}' class='latex' /> are closed subsets in <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />. By Urysohn&#8217;s Lemma, there exists a <img src='http://s0.wp.com/latex.php?latex=%7Bg+%5Cin+C%28X+%5Crightarrow+%5B0%2C1%5D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g &#92;in C(X &#92;rightarrow [0,1])}' title='{g &#92;in C(X &#92;rightarrow [0,1])}' class='latex' /> such that <img src='http://s0.wp.com/latex.php?latex=%7Bg%28x%29%3D0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g(x)=0}' title='{g(x)=0}' class='latex' /> and <img src='http://s0.wp.com/latex.php?latex=%7Bg%28y%29%3D1%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g(y)=1}' title='{g(y)=1}' class='latex' />. Then <img src='http://s0.wp.com/latex.php?latex=%7B%28f%28x%29%29_%7Bf+%5Cin+C%28X+%5Crightarrow+%5B0%2C1%5D%29%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{(f(x))_{f &#92;in C(X &#92;rightarrow [0,1])}}' title='{(f(x))_{f &#92;in C(X &#92;rightarrow [0,1])}}' class='latex' /> and <img src='http://s0.wp.com/latex.php?latex=%7B%28f%28y%29%29_%7Bf+%5Cin+C%28X+%5Crightarrow+%5B0%2C1%5D%29%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{(f(y))_{f &#92;in C(X &#92;rightarrow [0,1])}}' title='{(f(y))_{f &#92;in C(X &#92;rightarrow [0,1])}}' class='latex' />, these two tuples disagree at the <img src='http://s0.wp.com/latex.php?latex=%7Bg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g}' title='{g}' class='latex' />-th coordinate. Therefore <img src='http://s0.wp.com/latex.php?latex=%7Bi%28x%29+%5Cneq+i%28y%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i(x) &#92;neq i(y)}' title='{i(x) &#92;neq i(y)}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7Bi%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i}' title='{i}' class='latex' /> is injective, and therefore a bijection between <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> and <img src='http://s0.wp.com/latex.php?latex=%7Bi%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i(X)}' title='{i(X)}' class='latex' />.</p>
<p>We consider <img src='http://s0.wp.com/latex.php?latex=%7Bi%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i(X)}' title='{i(X)}' class='latex' /> to have the subspace topology as a subset of <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' />, and we consider <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' /> to have the subspace topology as a subset of <img src='http://s0.wp.com/latex.php?latex=%7BQ%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{Q}' title='{Q}' class='latex' />. This is exactly the same topology as the subspace topology of <img src='http://s0.wp.com/latex.php?latex=%7Bi%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i(X)}' title='{i(X)}' class='latex' /> when considered as a subset of <img src='http://s0.wp.com/latex.php?latex=%7BQ%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{Q}' title='{Q}' class='latex' />. Thus, <img src='http://s0.wp.com/latex.php?latex=%7BQ%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{Q}' title='{Q}' class='latex' /> inherits the topology of point-wise-convergence. Now to show that <img src='http://s0.wp.com/latex.php?latex=%7Bi%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i}' title='{i}' class='latex' /> is continuous. Suppose we&#8217;re given any net in <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7Bx_%5Calpha%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{x_&#92;alpha&#92;}}' title='{&#92;{x_&#92;alpha&#92;}}' class='latex' /> in <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> that converges to some point <img src='http://s0.wp.com/latex.php?latex=%7Bx+%5Cin+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x &#92;in X}' title='{x &#92;in X}' class='latex' />. Consider <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7Bi%28x_%5Calpha%29%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{i(x_&#92;alpha)&#92;}}' title='{&#92;{i(x_&#92;alpha)&#92;}}' class='latex' /> in <img src='http://s0.wp.com/latex.php?latex=%7Bi%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i(X)}' title='{i(X)}' class='latex' />, we need to show that this net converges to <img src='http://s0.wp.com/latex.php?latex=%7Bi%28x%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i(x)}' title='{i(x)}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7Bi%28x_%5Calpha%29%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{i(x_&#92;alpha)&#92;}}' title='{&#92;{i(x_&#92;alpha)&#92;}}' class='latex' /> converges to <img src='http://s0.wp.com/latex.php?latex=%7Bi%28x%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i(x)}' title='{i(x)}' class='latex' /> if and only if <img src='http://s0.wp.com/latex.php?latex=%7Bf%28x_%5Calpha%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f(x_&#92;alpha)}' title='{f(x_&#92;alpha)}' class='latex' /> converges to <img src='http://s0.wp.com/latex.php?latex=%7Bf%28x%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f(x)}' title='{f(x)}' class='latex' /> for all <img src='http://s0.wp.com/latex.php?latex=%7Bf+%5Cin+C%28X+%5Crightarrow+%5B0%2C1%5D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f &#92;in C(X &#92;rightarrow [0,1])}' title='{f &#92;in C(X &#92;rightarrow [0,1])}' class='latex' />. For each <img src='http://s0.wp.com/latex.php?latex=%7Bf+%5Cin+C%28X+%5Crightarrow+%5B0%2C1%5D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f &#92;in C(X &#92;rightarrow [0,1])}' title='{f &#92;in C(X &#92;rightarrow [0,1])}' class='latex' />, we have that the net <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7Bf%28x_%5Calpha%29%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{f(x_&#92;alpha)&#92;}}' title='{&#92;{f(x_&#92;alpha)&#92;}}' class='latex' /> converges to <img src='http://s0.wp.com/latex.php?latex=%7Bf%28x%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f(x)}' title='{f(x)}' class='latex' /> since each <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' /> is continuous. The net <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7Bi%28x_%5Calpha%29%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{i(x_&#92;alpha)&#92;}}' title='{&#92;{i(x_&#92;alpha)&#92;}}' class='latex' /> converges point-wise to <img src='http://s0.wp.com/latex.php?latex=%7Bi%28x%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i(x)}' title='{i(x)}' class='latex' />, and therefore converges to <img src='http://s0.wp.com/latex.php?latex=%7Bi%28x%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i(x)}' title='{i(x)}' class='latex' /> in the product topology <img src='http://s0.wp.com/latex.php?latex=%7Bi%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i(X)}' title='{i(X)}' class='latex' /> inherits from <img src='http://s0.wp.com/latex.php?latex=%7BQ%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{Q}' title='{Q}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7Bi%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i}' title='{i}' class='latex' /> is continuous at <img src='http://s0.wp.com/latex.php?latex=%7Bx%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x}' title='{x}' class='latex' />, and since our choice of <img src='http://s0.wp.com/latex.php?latex=%7Bx%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x}' title='{x}' class='latex' /> was arbitrary, <img src='http://s0.wp.com/latex.php?latex=%7Bi%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i}' title='{i}' class='latex' /> is a continuous on <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />.</p>
<p>Now let&#8217;s show that <img src='http://s0.wp.com/latex.php?latex=%7Bi%5E%7B-1%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i^{-1}}' title='{i^{-1}}' class='latex' /> is continuous. Suppose that the net <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7Bi%28x_%5Calpha%29%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{i(x_&#92;alpha)&#92;}}' title='{&#92;{i(x_&#92;alpha)&#92;}}' class='latex' /> in <img src='http://s0.wp.com/latex.php?latex=%7Bi%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i(X)}' title='{i(X)}' class='latex' /> converges to some point <img src='http://s0.wp.com/latex.php?latex=%7Bi%28x%29+%5Cin+i%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i(x) &#92;in i(X)}' title='{i(x) &#92;in i(X)}' class='latex' />, then we need to show that the net <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7Bx_%5Calpha%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{x_&#92;alpha&#92;}}' title='{&#92;{x_&#92;alpha&#92;}}' class='latex' /> converges to <img src='http://s0.wp.com/latex.php?latex=%7Bx%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x}' title='{x}' class='latex' /> in <img src='http://s0.wp.com/latex.php?latex=%7B%5B0%2C1%5D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{[0,1]}' title='{[0,1]}' class='latex' />. Let <img src='http://s0.wp.com/latex.php?latex=%7BU%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U}' title='{U}' class='latex' /> be an open set in <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> containing <img src='http://s0.wp.com/latex.php?latex=%7Bx%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x}' title='{x}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> is a locally compact Hausdorff space, and we can appeal to the generalized version of the Urysohn&#8217;s Lemma we proved in Exercise 6 in Notes 12. So we can find some <img src='http://s0.wp.com/latex.php?latex=%7Bg+%5Cin+C%28X+%5Crightarrow+%5B0%2C1%5D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g &#92;in C(X &#92;rightarrow [0,1])}' title='{g &#92;in C(X &#92;rightarrow [0,1])}' class='latex' /> such that <img src='http://s0.wp.com/latex.php?latex=%7Bg%28x%29%3D1%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g(x)=1}' title='{g(x)=1}' class='latex' /> and <img src='http://s0.wp.com/latex.php?latex=%7Bg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g}' title='{g}' class='latex' /> vanishes outside a compact set that is contained in <img src='http://s0.wp.com/latex.php?latex=%7BU%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U}' title='{U}' class='latex' />. By assumption, <img src='http://s0.wp.com/latex.php?latex=%7Bg%28x_%5Calpha%29+%5Crightarrow+g%28x%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g(x_&#92;alpha) &#92;rightarrow g(x)}' title='{g(x_&#92;alpha) &#92;rightarrow g(x)}' class='latex' />, and thus there exists a <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta}' title='{&#92;beta}' class='latex' /> such that <img src='http://s0.wp.com/latex.php?latex=%7Bg%28x_%5Calpha%29+%5Cin+%280%2C1%5D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g(x_&#92;alpha) &#92;in (0,1]}' title='{g(x_&#92;alpha) &#92;in (0,1]}' class='latex' /> whenever <img src='http://s0.wp.com/latex.php?latex=%7B%5Calpha+%5Csucceq+%5Cbeta%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;alpha &#92;succeq &#92;beta}' title='{&#92;alpha &#92;succeq &#92;beta}' class='latex' />. The support of <img src='http://s0.wp.com/latex.php?latex=%7Bg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g}' title='{g}' class='latex' /> is contained in <img src='http://s0.wp.com/latex.php?latex=%7BU%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U}' title='{U}' class='latex' />, and therefore <img src='http://s0.wp.com/latex.php?latex=%7Bx_%5Calpha+%5Cin+U%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x_&#92;alpha &#92;in U}' title='{x_&#92;alpha &#92;in U}' class='latex' /> whenever <img src='http://s0.wp.com/latex.php?latex=%7B%5Calpha+%5Csucceq+%5Cbeta%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;alpha &#92;succeq &#92;beta}' title='{&#92;alpha &#92;succeq &#92;beta}' class='latex' />. We&#8217;ve shown directly that the net <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7Bx_%5Calpha%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{x_&#92;alpha&#92;}}' title='{&#92;{x_&#92;alpha&#92;}}' class='latex' /> converges to <img src='http://s0.wp.com/latex.php?latex=%7Bx%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x}' title='{x}' class='latex' />. Therefore, for any <img src='http://s0.wp.com/latex.php?latex=%7Bx+%5Cin+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x &#92;in X}' title='{x &#92;in X}' class='latex' />, we see that <img src='http://s0.wp.com/latex.php?latex=%7Bx_%5Calpha+%5Crightarrow+x%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x_&#92;alpha &#92;rightarrow x}' title='{x_&#92;alpha &#92;rightarrow x}' class='latex' /> whenever <img src='http://s0.wp.com/latex.php?latex=%7Bi%28x_%5Calpha%29+%5Crightarrow+i%28x%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i(x_&#92;alpha) &#92;rightarrow i(x)}' title='{i(x_&#92;alpha) &#92;rightarrow i(x)}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7Bi%5E%7B-1%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i^{-1}}' title='{i^{-1}}' class='latex' /> is continuous.</p>
<p>By construction, <img src='http://s0.wp.com/latex.php?latex=%7Bi%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i(X)}' title='{i(X)}' class='latex' /> is dense in <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' />. So all we need to do is show that <img src='http://s0.wp.com/latex.php?latex=%7Bi%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i(X)}' title='{i(X)}' class='latex' /> is open in <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' />. Pick an <img src='http://s0.wp.com/latex.php?latex=%7Bx+%5Cin+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x &#92;in X}' title='{x &#92;in X}' class='latex' />. Since <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> is a locally compact Hausdorff space, we know there exists a function <img src='http://s0.wp.com/latex.php?latex=%7Bf+%3AX+%5Crightarrow+%5B0%2C1%5D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f :X &#92;rightarrow [0,1]}' title='{f :X &#92;rightarrow [0,1]}' class='latex' /> if compact support (say the support is <img src='http://s0.wp.com/latex.php?latex=%7BF%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{F}' title='{F}' class='latex' />) that is 1 at <img src='http://s0.wp.com/latex.php?latex=%7Bx%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x}' title='{x}' class='latex' />. Consider <img src='http://s0.wp.com/latex.php?latex=%7Bi+%28x%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i (x)}' title='{i (x)}' class='latex' />. Consider all <img src='http://s0.wp.com/latex.php?latex=%7By+%5Cin+%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{y &#92;in &#92;beta X}' title='{y &#92;in &#92;beta X}' class='latex' /> such that <img src='http://s0.wp.com/latex.php?latex=%7By_f+%3E+%5Cfrac%7B1%7D%7B2%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{y_f &gt; &#92;frac{1}{2}}' title='{y_f &gt; &#92;frac{1}{2}}' class='latex' />, this is clearly an open set in <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' /> that contains <img src='http://s0.wp.com/latex.php?latex=%7Bx%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x}' title='{x}' class='latex' />. Suppose that we&#8217;re given a <img src='http://s0.wp.com/latex.php?latex=%7Bz+%5Cin+%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{z &#92;in &#92;beta X}' title='{z &#92;in &#92;beta X}' class='latex' /> that is not in <img src='http://s0.wp.com/latex.php?latex=%7Bi%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i(X)}' title='{i(X)}' class='latex' />. If we show that <img src='http://s0.wp.com/latex.php?latex=%7Bz_f+%3D0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{z_f =0}' title='{z_f =0}' class='latex' />, then <img src='http://s0.wp.com/latex.php?latex=%7Bz%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{z}' title='{z}' class='latex' /> can&#8217;t be in the set of all <img src='http://s0.wp.com/latex.php?latex=%7By%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{y}' title='{y}' class='latex' /> such that <img src='http://s0.wp.com/latex.php?latex=%7By_f+%3E+%5Cfrac%7B1%7D%7B2%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{y_f &gt; &#92;frac{1}{2}}' title='{y_f &gt; &#92;frac{1}{2}}' class='latex' />. Thus, the contrapositive would be true, and we&#8217;ve found an open set in <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' /> around <img src='http://s0.wp.com/latex.php?latex=%7Bi%28x%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i(x)}' title='{i(x)}' class='latex' /> that is contained in <img src='http://s0.wp.com/latex.php?latex=%7Bi%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i(X)}' title='{i(X)}' class='latex' />. Let <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7Bi%28x_%5Calpha%29%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{i(x_&#92;alpha)&#92;}}' title='{&#92;{i(x_&#92;alpha)&#92;}}' class='latex' /> be a net that converges to <img src='http://s0.wp.com/latex.php?latex=%7Bz%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{z}' title='{z}' class='latex' />. Then there must be a <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta}' title='{&#92;beta}' class='latex' /> such that <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7Bx_%5Calpha%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{x_&#92;alpha&#92;}}' title='{&#92;{x_&#92;alpha&#92;}}' class='latex' /> lies in <img src='http://s0.wp.com/latex.php?latex=%7BF%5Ec%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{F^c}' title='{F^c}' class='latex' /> for all <img src='http://s0.wp.com/latex.php?latex=%7B%5Calpha+%5Csucceq+%5Cbeta%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;alpha &#92;succeq &#92;beta}' title='{&#92;alpha &#92;succeq &#92;beta}' class='latex' />, or we could construct a convergent subset that lies entirely within <img src='http://s0.wp.com/latex.php?latex=%7BF%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{F}' title='{F}' class='latex' />. But since <img src='http://s0.wp.com/latex.php?latex=%7BF%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{F}' title='{F}' class='latex' /> is compact, that net would converge to a point in <img src='http://s0.wp.com/latex.php?latex=%7BF%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{F}' title='{F}' class='latex' />, contradicting our choice of <img src='http://s0.wp.com/latex.php?latex=%7Bz%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{z}' title='{z}' class='latex' />. If <img src='http://s0.wp.com/latex.php?latex=%7Bz_f+%3E+0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{z_f &gt; 0}' title='{z_f &gt; 0}' class='latex' />, then choose the open set in <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' /> consisting of all points such that <img src='http://s0.wp.com/latex.php?latex=%7By_f+%3E+%5Cfrac%7Bz_f%7D%7B2%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{y_f &gt; &#92;frac{z_f}{2}}' title='{y_f &gt; &#92;frac{z_f}{2}}' class='latex' /> intersect <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' />. Then this is an open set around <img src='http://s0.wp.com/latex.php?latex=%7Bz%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{z}' title='{z}' class='latex' />, but <img src='http://s0.wp.com/latex.php?latex=%7Bf%28x_%5Calpha%29%3D0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f(x_&#92;alpha)=0}' title='{f(x_&#92;alpha)=0}' class='latex' /> whenever <img src='http://s0.wp.com/latex.php?latex=%7B%5Calpha+%5Csucceq+%5Cbeta%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;alpha &#92;succeq &#92;beta}' title='{&#92;alpha &#92;succeq &#92;beta}' class='latex' />, which contradicts that <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7Bi%28x_%5Calpha%29%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{i(x_&#92;alpha)&#92;}}' title='{&#92;{i(x_&#92;alpha)&#92;}}' class='latex' /> converges to <img src='http://s0.wp.com/latex.php?latex=%7Bz%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{z}' title='{z}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7Bz_f%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{z_f}' title='{z_f}' class='latex' /> must be 0, and therefore we&#8217;ve shown that any point in <img src='http://s0.wp.com/latex.php?latex=%7Bi%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i(X)}' title='{i(X)}' class='latex' /> is an interior point of <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7Bi%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i(X)}' title='{i(X)}' class='latex' /> is open relative to <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' /> is indeed a compactification of <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />.</p>
<p><strong> Bullet Point Two </strong></p>
<p>Let <img src='http://s0.wp.com/latex.php?latex=%7Bi%3AX+%5Crightarrow+%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i:X &#92;rightarrow &#92;beta X}' title='{i:X &#92;rightarrow &#92;beta X}' class='latex' /> be the compactification defined above, and let <img src='http://s0.wp.com/latex.php?latex=%7Bj%3A+X+%5Crightarrow+%5Coverline%7BX%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{j: X &#92;rightarrow &#92;overline{X}}' title='{j: X &#92;rightarrow &#92;overline{X}}' class='latex' /> be some other compactification, and identify <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> as a subspace of <img src='http://s0.wp.com/latex.php?latex=%7B%5Coverline%7BX%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;overline{X}}' title='{&#92;overline{X}}' class='latex' />. Given a <img src='http://s0.wp.com/latex.php?latex=%7Bf+%5Cin+C%28%5Coverline%7BX%7D+%5Crightarrow+%5B0%2C1%5D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f &#92;in C(&#92;overline{X} &#92;rightarrow [0,1])}' title='{f &#92;in C(&#92;overline{X} &#92;rightarrow [0,1])}' class='latex' />, then the restriction map <img src='http://s0.wp.com/latex.php?latex=%7Bf+%5Crightarrow+f%7C_X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f &#92;rightarrow f|_X}' title='{f &#92;rightarrow f|_X}' class='latex' /> is a function from <img src='http://s0.wp.com/latex.php?latex=%7BC%28%5Coverline%7BX%7D+%5Crightarrow+%5B0%2C1%5D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C(&#92;overline{X} &#92;rightarrow [0,1])}' title='{C(&#92;overline{X} &#92;rightarrow [0,1])}' class='latex' />, and since <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> is dense, if <img src='http://s0.wp.com/latex.php?latex=%7Bf%7C_K+%3D+g%7C_K%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f|_K = g|_K}' title='{f|_K = g|_K}' class='latex' />, then <img src='http://s0.wp.com/latex.php?latex=%7Bf%3Dg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f=g}' title='{f=g}' class='latex' />. So our restriction map is injective, and therefore we can identify <img src='http://s0.wp.com/latex.php?latex=%7BC%28%5Coverline%7BX%7D%5Crightarrow+%5B0%2C1%5D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C(&#92;overline{X}&#92;rightarrow [0,1])}' title='{C(&#92;overline{X}&#92;rightarrow [0,1])}' class='latex' /> as a subspace of <img src='http://s0.wp.com/latex.php?latex=%7BC%28X+%5Crightarrow+%5B0%2C1%5D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C(X &#92;rightarrow [0,1])}' title='{C(X &#92;rightarrow [0,1])}' class='latex' />.</p>
<p>Consider the natural projection <img src='http://s0.wp.com/latex.php?latex=%7B%5Cpi%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;pi}' title='{&#92;pi}' class='latex' /> from <img src='http://s0.wp.com/latex.php?latex=%7BQ%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{Q}' title='{Q}' class='latex' /> to <img src='http://s0.wp.com/latex.php?latex=%7B%7B%5B0%2C1%5D%7D%5E%7BC%28%5Coverline%7BX%7D+%5Crightarrow+%5B0%2C1%5D%29%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{{[0,1]}^{C(&#92;overline{X} &#92;rightarrow [0,1])}}' title='{{[0,1]}^{C(&#92;overline{X} &#92;rightarrow [0,1])}}' class='latex' /> where we consider <img src='http://s0.wp.com/latex.php?latex=%7BC%28%5Coverline%7BX%7D+%5Crightarrow+%5B0%2C1%5D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C(&#92;overline{X} &#92;rightarrow [0,1])}' title='{C(&#92;overline{X} &#92;rightarrow [0,1])}' class='latex' /> as a subset of <img src='http://s0.wp.com/latex.php?latex=%7BC%28X+%5Crightarrow+%5B0%2C1%5D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C(X &#92;rightarrow [0,1])}' title='{C(X &#92;rightarrow [0,1])}' class='latex' />. Let <img src='http://s0.wp.com/latex.php?latex=%7BU%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U}' title='{U}' class='latex' /> be a basic open set in <img src='http://s0.wp.com/latex.php?latex=%7B%7B%5B0%2C1%5D%7D%5E%7BC%28%5Coverline%7BX%7D+%5Crightarrow+%5B0%2C1%5D%29%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{{[0,1]}^{C(&#92;overline{X} &#92;rightarrow [0,1])}}' title='{{[0,1]}^{C(&#92;overline{X} &#92;rightarrow [0,1])}}' class='latex' />. That is, <img src='http://s0.wp.com/latex.php?latex=%7BU+%3D+%5Ctimes_%7Bf+%5Cin+C%28%5Coverline%7BX%7D+%5Crightarrow+%5B0%2C1%5D%29%7D+U_f%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U = &#92;times_{f &#92;in C(&#92;overline{X} &#92;rightarrow [0,1])} U_f}' title='{U = &#92;times_{f &#92;in C(&#92;overline{X} &#92;rightarrow [0,1])} U_f}' class='latex' /> where each <img src='http://s0.wp.com/latex.php?latex=%7BU_f%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U_f}' title='{U_f}' class='latex' /> is open in <img src='http://s0.wp.com/latex.php?latex=%7B%5B0%2C1%5D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{[0,1]}' title='{[0,1]}' class='latex' /> all but finitely many <img src='http://s0.wp.com/latex.php?latex=%7BU_f%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U_f}' title='{U_f}' class='latex' />&#8216;s are equal to <img src='http://s0.wp.com/latex.php?latex=%7B%5B0%2C1%5D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{[0,1]}' title='{[0,1]}' class='latex' />. Let <img src='http://s0.wp.com/latex.php?latex=%7BU_%7Bf_1%7D%2C%5Cldots%2CU_%7Bf_n%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U_{f_1},&#92;ldots,U_{f_n}}' title='{U_{f_1},&#92;ldots,U_{f_n}}' class='latex' /> be the subsets of <img src='http://s0.wp.com/latex.php?latex=%7B%5B0%2C1%5D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{[0,1]}' title='{[0,1]}' class='latex' /> that aren&#8217;t equal to <img src='http://s0.wp.com/latex.php?latex=%7B%5B0%2C1%5D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{[0,1]}' title='{[0,1]}' class='latex' />. Then <img src='http://s0.wp.com/latex.php?latex=%7B%5Cpi%5E%7B-1%7D%28U%29+%3D+%5Ctimes_%7Bf+%5Cin+C%28X+%5Crightarrow+%5B0%2C1%5D%29%7D+V_f%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;pi^{-1}(U) = &#92;times_{f &#92;in C(X &#92;rightarrow [0,1])} V_f}' title='{&#92;pi^{-1}(U) = &#92;times_{f &#92;in C(X &#92;rightarrow [0,1])} V_f}' class='latex' /> where <img src='http://s0.wp.com/latex.php?latex=%7BV_%7Bf_i%7D%3DU_%7Bf_i%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{V_{f_i}=U_{f_i}}' title='{V_{f_i}=U_{f_i}}' class='latex' /> for each <img src='http://s0.wp.com/latex.php?latex=%7B1+%5Cleq+i+%5Cleq+n%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{1 &#92;leq i &#92;leq n}' title='{1 &#92;leq i &#92;leq n}' class='latex' /> and <img src='http://s0.wp.com/latex.php?latex=%7BV_f+%3D+%5B0%2C1%5D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{V_f = [0,1]}' title='{V_f = [0,1]}' class='latex' /> for all other <img src='http://s0.wp.com/latex.php?latex=%7Bf+%5Cin+C%28X+%5Crightarrow+%5B0%2C1%5D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f &#92;in C(X &#92;rightarrow [0,1])}' title='{f &#92;in C(X &#92;rightarrow [0,1])}' class='latex' />, thus <img src='http://s0.wp.com/latex.php?latex=%7B%5Cpi%5E%7B-1%7D%28U%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;pi^{-1}(U)}' title='{&#92;pi^{-1}(U)}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7B%5Cpi%5E%7B-1%7D%28U%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;pi^{-1}(U)}' title='{&#92;pi^{-1}(U)}' class='latex' /> is open whenever <img src='http://s0.wp.com/latex.php?latex=%7BU%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U}' title='{U}' class='latex' /> is a basic open set, and therefore <img src='http://s0.wp.com/latex.php?latex=%7B%5Cpi%5E%7B-1%7D%28U%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;pi^{-1}(U)}' title='{&#92;pi^{-1}(U)}' class='latex' /> is open whenever <img src='http://s0.wp.com/latex.php?latex=%7BU%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U}' title='{U}' class='latex' /> is open. <img src='http://s0.wp.com/latex.php?latex=%7B%5Cpi%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;pi}' title='{&#92;pi}' class='latex' /> is continuous. Let <img src='http://s0.wp.com/latex.php?latex=%7B%5Cpi%5E%5Cprime%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;pi^&#92;prime}' title='{&#92;pi^&#92;prime}' class='latex' /> be the restriction of <img src='http://s0.wp.com/latex.php?latex=%7B%5Cpi%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;pi}' title='{&#92;pi}' class='latex' /> to <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' />. The image of <img src='http://s0.wp.com/latex.php?latex=%7B%5Cpi%5E%5Cprime%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;pi^&#92;prime}' title='{&#92;pi^&#92;prime}' class='latex' /> is the image of <img src='http://s0.wp.com/latex.php?latex=%7B%5Coverline%7BX%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;overline{X}}' title='{&#92;overline{X}}' class='latex' /> inside <img src='http://s0.wp.com/latex.php?latex=%7B%7B%5B0%2C1%5D%7D%5E%7BC%28%5Coverline%7BX%7D+%5Crightarrow+%5B0%2C1%5D%29%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{{[0,1]}^{C(&#92;overline{X} &#92;rightarrow [0,1])}}' title='{{[0,1]}^{C(&#92;overline{X} &#92;rightarrow [0,1])}}' class='latex' /> by the Gelfand transformation. So we can consider <img src='http://s0.wp.com/latex.php?latex=%7B%5Cpi%5E%5Cprime%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;pi^&#92;prime}' title='{&#92;pi^&#92;prime}' class='latex' /> to be a continuous function from <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' /> to <img src='http://s0.wp.com/latex.php?latex=%7B%5Coverline%7BX%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;overline{X}}' title='{&#92;overline{X}}' class='latex' />. We need to show that <img src='http://s0.wp.com/latex.php?latex=%7Bj+%3D+%5Cpi%5E%5Cprime+%5Ccirc+i%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{j = &#92;pi^&#92;prime &#92;circ i}' title='{j = &#92;pi^&#92;prime &#92;circ i}' class='latex' />. Pick a <img src='http://s0.wp.com/latex.php?latex=%7Bx+%5Cin+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x &#92;in X}' title='{x &#92;in X}' class='latex' />, then <img src='http://s0.wp.com/latex.php?latex=%7Bj%28x%29%3Dx%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{j(x)=x}' title='{j(x)=x}' class='latex' /> since we&#8217;re considering <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> to be a subset of <img src='http://s0.wp.com/latex.php?latex=%7B%5Coverline%7BX%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;overline{X}}' title='{&#92;overline{X}}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7B%5Cpi%5E%5Cprime%28i%28x%29%29%3D+%28f%28x%29%29_%7Bf+%5Cin+C%28%5Coverline%7BX%7D+%5Crightarrow+%5B0%2C1%5D%29%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;pi^&#92;prime(i(x))= (f(x))_{f &#92;in C(&#92;overline{X} &#92;rightarrow [0,1])}}' title='{&#92;pi^&#92;prime(i(x))= (f(x))_{f &#92;in C(&#92;overline{X} &#92;rightarrow [0,1])}}' class='latex' />, which is the image of <img src='http://s0.wp.com/latex.php?latex=%7Bx%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x}' title='{x}' class='latex' /> under the Gelfand transformation. Thus, when we associate <img src='http://s0.wp.com/latex.php?latex=%7B%5Coverline%7BX%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;overline{X}}' title='{&#92;overline{X}}' class='latex' /> with it&#8217;s image under the Gelfand transformation, <img src='http://s0.wp.com/latex.php?latex=%7B%28%5Cpi%5E%5Cprime+%5Ccirc+i%29%28x%29%3Dx%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{(&#92;pi^&#92;prime &#92;circ i)(x)=x}' title='{(&#92;pi^&#92;prime &#92;circ i)(x)=x}' class='latex' />. Therefore <img src='http://s0.wp.com/latex.php?latex=%7Bi%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i}' title='{i}' class='latex' /> is finer than <img src='http://s0.wp.com/latex.php?latex=%7Bj%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{j}' title='{j}' class='latex' />, and since <img src='http://s0.wp.com/latex.php?latex=%7Bj%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{j}' title='{j}' class='latex' /> was an arbitrary compactification, <img src='http://s0.wp.com/latex.php?latex=%7Bi%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{i}' title='{i}' class='latex' /> must be the Stone-Cech compactification.</p>
<p><strong> Exercise 4 </strong></p>
<p><strong> Bullet Point One </strong></p>
<p>Let <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> be a space with discrete topology, and let <img src='http://s0.wp.com/latex.php?latex=%7B2%5EX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{2^X}' title='{2^X}' class='latex' /> be the Boolean algebra of all subsets of <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> (this is also the topology on <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />). By Stone&#8217;s Representation Theorem, <img src='http://s0.wp.com/latex.php?latex=%7B2%5EX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{2^X}' title='{2^X}' class='latex' /> is isomorphic to the clopen algebra of a Stone space, a totally disconnected compact Hausdorff space. Denote the clopen algebra by <img src='http://s0.wp.com/latex.php?latex=%7BCl%28%5Cbeta+X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{Cl(&#92;beta X)}' title='{Cl(&#92;beta X)}' class='latex' />. Denote the isomorphism between <img src='http://s0.wp.com/latex.php?latex=%7B2%5EX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{2^X}' title='{2^X}' class='latex' /> and <img src='http://s0.wp.com/latex.php?latex=%7BCl%28%5Cbeta+X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{Cl(&#92;beta X)}' title='{Cl(&#92;beta X)}' class='latex' /> by <img src='http://s0.wp.com/latex.php?latex=%7B%5Cphi%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;phi}' title='{&#92;phi}' class='latex' />.</p>
<p>For each <img src='http://s0.wp.com/latex.php?latex=%7Bx+%5Cin+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x &#92;in X}' title='{x &#92;in X}' class='latex' />, <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7Bx%5C%7D+%5Cin+2%5EX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{x&#92;} &#92;in 2^X}' title='{&#92;{x&#92;} &#92;in 2^X}' class='latex' />, and consider <img src='http://s0.wp.com/latex.php?latex=%7B%5Cphi%28%5C%7Bx%5C%7D%29+%5Cin+Cl%28%5Cbeta+X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;phi(&#92;{x&#92;}) &#92;in Cl(&#92;beta X)}' title='{&#92;phi(&#92;{x&#92;}) &#92;in Cl(&#92;beta X)}' class='latex' />. Fix <img src='http://s0.wp.com/latex.php?latex=%7By+%5Cin+%5Cphi%28%5C%7Bx%5C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{y &#92;in &#92;phi(&#92;{x&#92;})}' title='{y &#92;in &#92;phi(&#92;{x&#92;})}' class='latex' />. In order to find a embedding from <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> to <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' />, we need to show that <img src='http://s0.wp.com/latex.php?latex=%7B%5Cphi%28%5C%7Bx%5C%7D%29%3D%5C%7By%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;phi(&#92;{x&#92;})=&#92;{y&#92;}}' title='{&#92;phi(&#92;{x&#92;})=&#92;{y&#92;}}' class='latex' />. Suppose there is a strictly smaller clopen set that contains <img src='http://s0.wp.com/latex.php?latex=%7By%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{y}' title='{y}' class='latex' />, denote it by <img src='http://s0.wp.com/latex.php?latex=%7BU%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U}' title='{U}' class='latex' />. But <img src='http://s0.wp.com/latex.php?latex=%7B%5Cphi%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;phi}' title='{&#92;phi}' class='latex' /> is an isomorphism, so <img src='http://s0.wp.com/latex.php?latex=%7B%5Cphi%5E%7B-1%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;phi^{-1}}' title='{&#92;phi^{-1}}' class='latex' /> exists and preserves orderings. Thus <img src='http://s0.wp.com/latex.php?latex=%7B%5Cphi%5E%7B-1%7D%28U%29+%5Csubset+%5Cphi%5E%7B-1%7D%28%5Cphi%28%5C%7Bx%5C%7D%29%29%3D%5C%7Bx%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;phi^{-1}(U) &#92;subset &#92;phi^{-1}(&#92;phi(&#92;{x&#92;}))=&#92;{x&#92;}}' title='{&#92;phi^{-1}(U) &#92;subset &#92;phi^{-1}(&#92;phi(&#92;{x&#92;}))=&#92;{x&#92;}}' class='latex' />. If <img src='http://s0.wp.com/latex.php?latex=%7B%5Cphi%5E%7B-1%7D%28U%29+%3D+%5C%7Bx%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;phi^{-1}(U) = &#92;{x&#92;}}' title='{&#92;phi^{-1}(U) = &#92;{x&#92;}}' class='latex' />, then <img src='http://s0.wp.com/latex.php?latex=%7BU+%3D+%5Cphi%28%5C%7Bx%5C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U = &#92;phi(&#92;{x&#92;})}' title='{U = &#92;phi(&#92;{x&#92;})}' class='latex' /> which contradicts our assumption that <img src='http://s0.wp.com/latex.php?latex=%7BU%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U}' title='{U}' class='latex' /> is strictly smaller than <img src='http://s0.wp.com/latex.php?latex=%7B%5Cphi%28%5C%7Bx%5C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;phi(&#92;{x&#92;})}' title='{&#92;phi(&#92;{x&#92;})}' class='latex' />. If <img src='http://s0.wp.com/latex.php?latex=%7B%5Cphi%5E%7B-1%7D%28U%29+%3D+%5Cemptyset%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;phi^{-1}(U) = &#92;emptyset}' title='{&#92;phi^{-1}(U) = &#92;emptyset}' class='latex' />, then <img src='http://s0.wp.com/latex.php?latex=%7BU+%3D+%5Cemptyset%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U = &#92;emptyset}' title='{U = &#92;emptyset}' class='latex' />, which contradicts our assumption that <img src='http://s0.wp.com/latex.php?latex=%7BU%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U}' title='{U}' class='latex' /> contains <img src='http://s0.wp.com/latex.php?latex=%7By%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{y}' title='{y}' class='latex' />. We&#8217;ve exhausted our cases, <img src='http://s0.wp.com/latex.php?latex=%7B%5Cphi%5E%7B-1%7D%28U%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;phi^{-1}(U)}' title='{&#92;phi^{-1}(U)}' class='latex' /> is the smallest clopen set that contains <img src='http://s0.wp.com/latex.php?latex=%7By%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{y}' title='{y}' class='latex' />. We haven&#8217;t yet shown that <img src='http://s0.wp.com/latex.php?latex=%7B%5Cphi%28%5C%7Bx%5C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;phi(&#92;{x&#92;})}' title='{&#92;phi(&#92;{x&#92;})}' class='latex' /> is the singleton set that contains <img src='http://s0.wp.com/latex.php?latex=%7By%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{y}' title='{y}' class='latex' />, we have one more step. The proof of Lemma 1 in Notes 4 shows that the intersection of all clopen sets that contain <img src='http://s0.wp.com/latex.php?latex=%7By%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{y}' title='{y}' class='latex' /> is <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7By%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{y&#92;}}' title='{&#92;{y&#92;}}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7B%5Cphi%28%5C%7Bx%5C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;phi(&#92;{x&#92;})}' title='{&#92;phi(&#92;{x&#92;})}' class='latex' /> is a subset of any clopen set that contains <img src='http://s0.wp.com/latex.php?latex=%7By%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{y}' title='{y}' class='latex' />, and thus lies in the intersection of all clopen sets that contain <img src='http://s0.wp.com/latex.php?latex=%7By%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{y}' title='{y}' class='latex' />. Therefore <img src='http://s0.wp.com/latex.php?latex=%7B%5Cphi%28%5C%7Bx%5C%7D%29%3D%5C%7By%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;phi(&#92;{x&#92;})=&#92;{y&#92;}}' title='{&#92;phi(&#92;{x&#92;})=&#92;{y&#92;}}' class='latex' />.</p>
<p>Now we can define our compactification. Consider the map <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%3A+X+%5Crightarrow+%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota: X &#92;rightarrow &#92;beta X}' title='{&#92;iota: X &#92;rightarrow &#92;beta X}' class='latex' /> where <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota+%28x%29+%3D+y%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota (x) = y}' title='{&#92;iota (x) = y}' class='latex' /> where <img src='http://s0.wp.com/latex.php?latex=%7B%5Cphi%28%5C%7Bx%5C%7D%29+%3D+%5C%7By%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;phi(&#92;{x&#92;}) = &#92;{y&#92;}}' title='{&#92;phi(&#92;{x&#92;}) = &#92;{y&#92;}}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota}' title='{&#92;iota}' class='latex' /> is an injection because if <img src='http://s0.wp.com/latex.php?latex=%7Bx_1+%5Cneq+x_2%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x_1 &#92;neq x_2}' title='{x_1 &#92;neq x_2}' class='latex' /> then <img src='http://s0.wp.com/latex.php?latex=%7B%5Cphi%28%5C%7Bx_1%5C%7D%29+%5Ccap+%5Cphi%28%5C%7Bx_2%5C%7D%29+%3D+%5Cphi%28%5C%7Bx_1%5C%7D+%5Ccap+%5C%7Bx_2%5C%7D%29+%3D+%5Cphi+%28%5Cemptyset%29+%3D+%5Cemptyset%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;phi(&#92;{x_1&#92;}) &#92;cap &#92;phi(&#92;{x_2&#92;}) = &#92;phi(&#92;{x_1&#92;} &#92;cap &#92;{x_2&#92;}) = &#92;phi (&#92;emptyset) = &#92;emptyset}' title='{&#92;phi(&#92;{x_1&#92;}) &#92;cap &#92;phi(&#92;{x_2&#92;}) = &#92;phi(&#92;{x_1&#92;} &#92;cap &#92;{x_2&#92;}) = &#92;phi (&#92;emptyset) = &#92;emptyset}' class='latex' />. Therefore if <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7By_1%5C%7D%3D%5Cphi%28x_1%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{y_1&#92;}=&#92;phi(x_1)}' title='{&#92;{y_1&#92;}=&#92;phi(x_1)}' class='latex' /> and <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7By_2%5C%7D%3D%5Cphi%28x_2%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{y_2&#92;}=&#92;phi(x_2)}' title='{&#92;{y_2&#92;}=&#92;phi(x_2)}' class='latex' />, then <img src='http://s0.wp.com/latex.php?latex=%7By_1+%5Cneq+y_2%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{y_1 &#92;neq y_2}' title='{y_1 &#92;neq y_2}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota}' title='{&#92;iota}' class='latex' /> is injective. Therefore <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota}' title='{&#92;iota}' class='latex' /> is a bijection between <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> and <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota+%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota (X)}' title='{&#92;iota (X)}' class='latex' />.</p>
<p>Let <img src='http://s0.wp.com/latex.php?latex=%7BU%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U}' title='{U}' class='latex' /> be open in <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota(X)}' title='{&#92;iota(X)}' class='latex' />, then <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%5E%7B-1%7D%28U%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota^{-1}(U)}' title='{&#92;iota^{-1}(U)}' class='latex' /> is some subset of <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />. But any subset is open in the discrete topology, therefore <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%5E%7B-1%7D%28U%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota^{-1}(U)}' title='{&#92;iota^{-1}(U)}' class='latex' /> is open. <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota}' title='{&#92;iota}' class='latex' /> is continuous. Now let <img src='http://s0.wp.com/latex.php?latex=%7BV%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{V}' title='{V}' class='latex' /> be an open set in <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />, then <img src='http://s0.wp.com/latex.php?latex=%7BV+%5Csubset+2%5EX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{V &#92;subset 2^X}' title='{V &#92;subset 2^X}' class='latex' />. Then <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%28V%29+%3D+%5Ccup_%7Bx+%5Cin+V%7D%5C%7B%5Ciota%28x%29%5C%7D%3D+%5Ccup_%7Bx+%5Cin+V%7D+%5Cphi%28%5C%7Bx%5C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota(V) = &#92;cup_{x &#92;in V}&#92;{&#92;iota(x)&#92;}= &#92;cup_{x &#92;in V} &#92;phi(&#92;{x&#92;})}' title='{&#92;iota(V) = &#92;cup_{x &#92;in V}&#92;{&#92;iota(x)&#92;}= &#92;cup_{x &#92;in V} &#92;phi(&#92;{x&#92;})}' class='latex' />. Each <img src='http://s0.wp.com/latex.php?latex=%7B%5Cphi%28%5C%7Bx%5C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;phi(&#92;{x&#92;})}' title='{&#92;phi(&#92;{x&#92;})}' class='latex' /> is a clopen set in <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' /> and a subset of <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota(X)}' title='{&#92;iota(X)}' class='latex' /> and therefore clopen relative to <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota(X)}' title='{&#92;iota(X)}' class='latex' />, and thus <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%28V%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota(V)}' title='{&#92;iota(V)}' class='latex' /> is the union of open sets and therefore open relative to <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota(X)}' title='{&#92;iota(X)}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%5E%7B-1%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota^{-1}}' title='{&#92;iota^{-1}}' class='latex' /> is continuous. <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota}' title='{&#92;iota}' class='latex' /> is a homeomorphism between <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> and <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota(X)}' title='{&#92;iota(X)}' class='latex' />. To finish our proof we need to show that <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota(X)}' title='{&#92;iota(X)}' class='latex' /> is a dense open subset of <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' />.</p>
<p><img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%28X%29+%3D+%5Ccup_%7Bx+%5Cin+X%7D%5Cphi%28%5C%7Bx%5C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota(X) = &#92;cup_{x &#92;in X}&#92;phi(&#92;{x&#92;})}' title='{&#92;iota(X) = &#92;cup_{x &#92;in X}&#92;phi(&#92;{x&#92;})}' class='latex' />, and as we said in the previous paragraph each <img src='http://s0.wp.com/latex.php?latex=%7B%5Cphi%28%5C%7Bx%5C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;phi(&#92;{x&#92;})}' title='{&#92;phi(&#92;{x&#92;})}' class='latex' /> is open in <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' />, and thus <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota(X)}' title='{&#92;iota(X)}' class='latex' /> is open in <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' />. Finally, to show that <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota(X)}' title='{&#92;iota(X)}' class='latex' /> is dense in <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' />. Pick a point <img src='http://s0.wp.com/latex.php?latex=%7Bz%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{z}' title='{z}' class='latex' /> in <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' />, and pick an open neighborhood <img src='http://s0.wp.com/latex.php?latex=%7BU%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U}' title='{U}' class='latex' /> around <img src='http://s0.wp.com/latex.php?latex=%7Bz%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{z}' title='{z}' class='latex' />. By Lemma 1 in Notes 4, the clopen algebra of <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' /> forms an open base for the topology, so there exists a clopen set <img src='http://s0.wp.com/latex.php?latex=%7BV%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{V}' title='{V}' class='latex' /> such that <img src='http://s0.wp.com/latex.php?latex=%7Bz+%5Cin+V%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{z &#92;in V}' title='{z &#92;in V}' class='latex' />. Pick some <img src='http://s0.wp.com/latex.php?latex=%7Bx+%5Cin+%5Cphi%5E%7B-1%7D%28V%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x &#92;in &#92;phi^{-1}(V)}' title='{x &#92;in &#92;phi^{-1}(V)}' class='latex' />, then let <img src='http://s0.wp.com/latex.php?latex=%7By+%3D+%5Ciota%28x%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{y = &#92;iota(x)}' title='{y = &#92;iota(x)}' class='latex' />, then <img src='http://s0.wp.com/latex.php?latex=%7By+%5Cin+V%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{y &#92;in V}' title='{y &#92;in V}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota+%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota (X)}' title='{&#92;iota (X)}' class='latex' /> is dense in <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' />. We have finished our proof. <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota+%3A+X+%5Crightarrow+%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota : X &#92;rightarrow &#92;beta X}' title='{&#92;iota : X &#92;rightarrow &#92;beta X}' class='latex' /> is a compactification.</p>
<p><strong> Bullet Point Two </strong></p>
<p><strong> Bullet Point Three </strong></p>
<p><strong> Exercise 5 </strong></p>
<p>The first bullet point is a consequence of the second one. So we&#8217;ll just prove the second one.</p>
<p><strong> Bullet Point Two </strong></p>
<p><img src='http://s0.wp.com/latex.php?latex=%7BBC%28X+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{BC(X &#92;rightarrow {&#92;mathbb C})}' title='{BC(X &#92;rightarrow {&#92;mathbb C})}' class='latex' /> is an normed complex algebra under the sup-norm. The space is commutative, and unital since it contains the constant function <img src='http://s0.wp.com/latex.php?latex=%7B1%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{1}' title='{1}' class='latex' />. The sup-norm is sub-multiplicative. Consider the map <img src='http://s0.wp.com/latex.php?latex=%7B%7B%7D%5E%2A%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{{}^*}' title='{{}^*}' class='latex' /> that maps <img src='http://s0.wp.com/latex.php?latex=%7Bf+%5Crightarrow+%5Coverline%7Bf%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f &#92;rightarrow &#92;overline{f}}' title='{f &#92;rightarrow &#92;overline{f}}' class='latex' />. This map is anti-linear, and since <img src='http://s0.wp.com/latex.php?latex=%7B%7Cf%7C%3D%7C%5Coverline%7Bf%7D%7C%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{|f|=|&#92;overline{f}|}' title='{|f|=|&#92;overline{f}|}' class='latex' /> it is norm-preserving. Also, <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7Cf%5E%2Af%5C%7C%3D%5Csup_%7Bx+%5Cin+X%7D%7C%5Coverline%7Bf%7D%28x%29f%28x%29%7C%3D%5Csup_%7Bx+%5Cin+X%7D%7Cf%28x%29%7C%5E2+%3D+%7B%28%5Csup_%7Bx+%5Cin+X%7D%7Cf%28x%29%7C%29%7D%5E2%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;|f^*f&#92;|=&#92;sup_{x &#92;in X}|&#92;overline{f}(x)f(x)|=&#92;sup_{x &#92;in X}|f(x)|^2 = {(&#92;sup_{x &#92;in X}|f(x)|)}^2}' title='{&#92;|f^*f&#92;|=&#92;sup_{x &#92;in X}|&#92;overline{f}(x)f(x)|=&#92;sup_{x &#92;in X}|f(x)|^2 = {(&#92;sup_{x &#92;in X}|f(x)|)}^2}' class='latex' />. So our space satisfies the <img src='http://s0.wp.com/latex.php?latex=%7BC%5E%2A%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C^*}' title='{C^*}' class='latex' />-identity.</p>
<p>Let <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' /> be the Stone-Cech compactification of <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />. Then <img src='http://s0.wp.com/latex.php?latex=%7BC%28%5Cbeta+X+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C(&#92;beta X &#92;rightarrow {&#92;mathbb C})}' title='{C(&#92;beta X &#92;rightarrow {&#92;mathbb C})}' class='latex' /> is a unital <img src='http://s0.wp.com/latex.php?latex=%7BC%5E%2A%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C^*}' title='{C^*}' class='latex' />-algebra when equipped with the sup-norm and with the anti-linear map <img src='http://s0.wp.com/latex.php?latex=%7Bf%5E%2A%3D%5Coverline%7Bf%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f^*=&#92;overline{f}}' title='{f^*=&#92;overline{f}}' class='latex' />. Consider the map <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%3A+C%28%5Cbeta+X+%5Crightarrow+%7B%5Cmathbb+C%7D%29+%5Crightarrow+C%28X+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota: C(&#92;beta X &#92;rightarrow {&#92;mathbb C}) &#92;rightarrow C(X &#92;rightarrow {&#92;mathbb C})}' title='{&#92;iota: C(&#92;beta X &#92;rightarrow {&#92;mathbb C}) &#92;rightarrow C(X &#92;rightarrow {&#92;mathbb C})}' class='latex' /> where <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota+%28f%29+%3D+f_X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota (f) = f_X}' title='{&#92;iota (f) = f_X}' class='latex' />. Since continuous functions on compact sets are bounded <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%28f%29+%5Cin+BC%28X+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota(f) &#92;in BC(X &#92;rightarrow {&#92;mathbb C})}' title='{&#92;iota(f) &#92;in BC(X &#92;rightarrow {&#92;mathbb C})}' class='latex' /> for each <img src='http://s0.wp.com/latex.php?latex=%7Bf+%5Cin+C%28%5Cbeta+X+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f &#92;in C(&#92;beta X &#92;rightarrow {&#92;mathbb C})}' title='{f &#92;in C(&#92;beta X &#92;rightarrow {&#92;mathbb C})}' class='latex' />. Consider <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota}' title='{&#92;iota}' class='latex' /> as a map between <img src='http://s0.wp.com/latex.php?latex=%7BC%28%5Cbeta+X+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C(&#92;beta X &#92;rightarrow {&#92;mathbb C})}' title='{C(&#92;beta X &#92;rightarrow {&#92;mathbb C})}' class='latex' /> and <img src='http://s0.wp.com/latex.php?latex=%7BBC%28X+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{BC(X &#92;rightarrow {&#92;mathbb C})}' title='{BC(X &#92;rightarrow {&#92;mathbb C})}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota}' title='{&#92;iota}' class='latex' /> is a homomorphism and it even preserve the anti-linear map. We need to show that <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota}' title='{&#92;iota}' class='latex' /> is a bijection and an isometry.</p>
<p>Since <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> is dense in <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' />, if we have <img src='http://s0.wp.com/latex.php?latex=%7Bf%2Cg+%5Cin+C%28%5Cbeta+X+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f,g &#92;in C(&#92;beta X &#92;rightarrow {&#92;mathbb C})}' title='{f,g &#92;in C(&#92;beta X &#92;rightarrow {&#92;mathbb C})}' class='latex' /> and <img src='http://s0.wp.com/latex.php?latex=%7Bf_X+%3D+g_X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f_X = g_X}' title='{f_X = g_X}' class='latex' /> then <img src='http://s0.wp.com/latex.php?latex=%7Bf%3Dg%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f=g}' title='{f=g}' class='latex' />. Thus, <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota}' title='{&#92;iota}' class='latex' /> is injective. Now if <img src='http://s0.wp.com/latex.php?latex=%7Bf+%5Cin+BC%28X+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f &#92;in BC(X &#92;rightarrow {&#92;mathbb C})}' title='{f &#92;in BC(X &#92;rightarrow {&#92;mathbb C})}' class='latex' />. Let <img src='http://s0.wp.com/latex.php?latex=%7BM%3D+%5C%7Cf%5C%7C%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{M= &#92;|f&#92;|}' title='{M= &#92;|f&#92;|}' class='latex' />, then <img src='http://s0.wp.com/latex.php?latex=%7Bf+%5Cin+BC%28X+%5Crightarrow+%5B-M%2CM%5D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f &#92;in BC(X &#92;rightarrow [-M,M])}' title='{f &#92;in BC(X &#92;rightarrow [-M,M])}' class='latex' />. Then by Exercise 2 in these notes, there exists a unique extension <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+f+%3A+%5Cbeta+X+%5Crightarrow+%5B-M%2CM%5D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta f : &#92;beta X &#92;rightarrow [-M,M]}' title='{&#92;beta f : &#92;beta X &#92;rightarrow [-M,M]}' class='latex' /> (since <img src='http://s0.wp.com/latex.php?latex=%7B%5B-M%2CM%5D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{[-M,M]}' title='{[-M,M]}' class='latex' /> is already compact) such that <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+f%7C_X+%3Df%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta f|_X =f}' title='{&#92;beta f|_X =f}' class='latex' />. Then <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+f+%5Cin+C%28%5Cbeta+X+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta f &#92;in C(&#92;beta X &#92;rightarrow {&#92;mathbb C})}' title='{&#92;beta f &#92;in C(&#92;beta X &#92;rightarrow {&#92;mathbb C})}' class='latex' /> and <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota+%28%5Cbeta+f%29+%3D+f%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota (&#92;beta f) = f}' title='{&#92;iota (&#92;beta f) = f}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota}' title='{&#92;iota}' class='latex' /> is surjective, and thus bijective.</p>
<p>Pick a <img src='http://s0.wp.com/latex.php?latex=%7Bf+%5Cin+C%28%5Cbeta+X+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f &#92;in C(&#92;beta X &#92;rightarrow {&#92;mathbb C})}' title='{f &#92;in C(&#92;beta X &#92;rightarrow {&#92;mathbb C})}' class='latex' />. Pick an <img src='http://s0.wp.com/latex.php?latex=%7Bx+%5Cin+%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x &#92;in &#92;beta X}' title='{x &#92;in &#92;beta X}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> is dense in <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' /> and therefore there exists a net <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7Bx_%5Calpha%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{x_&#92;alpha&#92;}}' title='{&#92;{x_&#92;alpha&#92;}}' class='latex' /> in <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> that converges to <img src='http://s0.wp.com/latex.php?latex=%7Bx%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x}' title='{x}' class='latex' />. Pick an <img src='http://s0.wp.com/latex.php?latex=%7B%5Cepsilon+%3E+0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;epsilon &gt; 0}' title='{&#92;epsilon &gt; 0}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' /> is continuous at <img src='http://s0.wp.com/latex.php?latex=%7Bx%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x}' title='{x}' class='latex' /> and therefore there exists a <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta}' title='{&#92;beta}' class='latex' /> such that <img src='http://s0.wp.com/latex.php?latex=%7B%7Cf%28x%29-f%28x_%5Calpha%29%7C%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{|f(x)-f(x_&#92;alpha)|}' title='{|f(x)-f(x_&#92;alpha)|}' class='latex' /> whenever <img src='http://s0.wp.com/latex.php?latex=%7B%5Calpha+%5Csucceq+%5Cbeta%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;alpha &#92;succeq &#92;beta}' title='{&#92;alpha &#92;succeq &#92;beta}' class='latex' />. Then if we pick an <img src='http://s0.wp.com/latex.php?latex=%7B%5Calpha+%5Csucceq+%5Cbeta%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;alpha &#92;succeq &#92;beta}' title='{&#92;alpha &#92;succeq &#92;beta}' class='latex' />, then we see that <img src='http://s0.wp.com/latex.php?latex=%7B%7Cf%28x%29%7C%5Cleq+%7Cf%28x%29-f%28x_%5Calpha%29%7C%2B%7Cf%28x_%5Calpha%29%7C++0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{|f(x)|&#92;leq |f(x)-f(x_&#92;alpha)|+|f(x_&#92;alpha)|  0}' title='{|f(x)|&#92;leq |f(x)-f(x_&#92;alpha)|+|f(x_&#92;alpha)|  0}' class='latex' />, we see that <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7Cf%5C%7C+%5Cleq+%5C%7C%5Ciota%28f%29%5C%7C%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;|f&#92;| &#92;leq &#92;|&#92;iota(f)&#92;|}' title='{&#92;|f&#92;| &#92;leq &#92;|&#92;iota(f)&#92;|}' class='latex' />. And since <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> is a subset of <img src='http://s0.wp.com/latex.php?latex=%7B%5Coverline%7BX%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;overline{X}}' title='{&#92;overline{X}}' class='latex' />, <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7C%5Ciota%7Bf%7D%5C%7C+%5Cleq+%5C%7Cf%5C%7C%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;|&#92;iota{f}&#92;| &#92;leq &#92;|f&#92;|}' title='{&#92;|&#92;iota{f}&#92;| &#92;leq &#92;|f&#92;|}' class='latex' />. Thus, <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota}' title='{&#92;iota}' class='latex' /> preserves norms.</p>
<p>We can now use this fact to show that <img src='http://s0.wp.com/latex.php?latex=%7BBC%28X+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{BC(X &#92;rightarrow {&#92;mathbb C})}' title='{BC(X &#92;rightarrow {&#92;mathbb C})}' class='latex' /> is complete, and therefore a <img src='http://s0.wp.com/latex.php?latex=%7BC%5E%2A%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C^*}' title='{C^*}' class='latex' />-algebra. Let <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7Bg_n%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{g_n&#92;}}' title='{&#92;{g_n&#92;}}' class='latex' /> be a Cauchy sequence in <img src='http://s0.wp.com/latex.php?latex=%7BBC%28X+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{BC(X &#92;rightarrow {&#92;mathbb C})}' title='{BC(X &#92;rightarrow {&#92;mathbb C})}' class='latex' />. Consider the sequence <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7Bf_n%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{f_n&#92;}}' title='{&#92;{f_n&#92;}}' class='latex' /> in <img src='http://s0.wp.com/latex.php?latex=%7BC%28%5Cbeta+X+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C(&#92;beta X &#92;rightarrow {&#92;mathbb C})}' title='{C(&#92;beta X &#92;rightarrow {&#92;mathbb C})}' class='latex' /> where <img src='http://s0.wp.com/latex.php?latex=%7Bg_n+%3D+%5Ciota+%28f_n%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g_n = &#92;iota (f_n)}' title='{g_n = &#92;iota (f_n)}' class='latex' />. Since <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota}' title='{&#92;iota}' class='latex' /> is a bijection that preserves norms, <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7Bf_n%5C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;{f_n&#92;}}' title='{&#92;{f_n&#92;}}' class='latex' /> is a Cauchy sequence in the complete space <img src='http://s0.wp.com/latex.php?latex=%7BC%28%5Cbeta+X+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C(&#92;beta X &#92;rightarrow {&#92;mathbb C})}' title='{C(&#92;beta X &#92;rightarrow {&#92;mathbb C})}' class='latex' /> and therefore converges to some <img src='http://s0.wp.com/latex.php?latex=%7Bf+%5Cin+C%28%5Cbeta+C+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f &#92;in C(&#92;beta C &#92;rightarrow {&#92;mathbb C})}' title='{f &#92;in C(&#92;beta C &#92;rightarrow {&#92;mathbb C})}' class='latex' />. Let <img src='http://s0.wp.com/latex.php?latex=%7Bg+%3D+%5Ciota+%28f%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{g = &#92;iota (f)}' title='{g = &#92;iota (f)}' class='latex' />. Since <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7Cf_n-f%5C%7C+%5Crightarrow+0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;|f_n-f&#92;| &#92;rightarrow 0}' title='{&#92;|f_n-f&#92;| &#92;rightarrow 0}' class='latex' />, and <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota}' title='{&#92;iota}' class='latex' /> is a homomorphism that is also an isometry, <img src='http://s0.wp.com/latex.php?latex=%7B%5C%7Cg_n+-g+%5C%7C+%5Crightarrow+0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;|g_n -g &#92;| &#92;rightarrow 0}' title='{&#92;|g_n -g &#92;| &#92;rightarrow 0}' class='latex' />. Every Cauchy sequence in <img src='http://s0.wp.com/latex.php?latex=%7BBC%28X+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{BC(X &#92;rightarrow {&#92;mathbb C})}' title='{BC(X &#92;rightarrow {&#92;mathbb C})}' class='latex' /> is a convergent sequence. <img src='http://s0.wp.com/latex.php?latex=%7BBC%28X+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{BC(X &#92;rightarrow {&#92;mathbb C})}' title='{BC(X &#92;rightarrow {&#92;mathbb C})}' class='latex' /> is complete, and therefore we have our last criteria met. <img src='http://s0.wp.com/latex.php?latex=%7BBC%28X+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{BC(X &#92;rightarrow {&#92;mathbb C})}' title='{BC(X &#92;rightarrow {&#92;mathbb C})}' class='latex' /> is a <img src='http://s0.wp.com/latex.php?latex=%7BC%5E%2A%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C^*}' title='{C^*}' class='latex' />-algebra and our map <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota}' title='{&#92;iota}' class='latex' /> is our <img src='http://s0.wp.com/latex.php?latex=%7BC%5E%2A%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C^*}' title='{C^*}' class='latex' />-isomorphism between <img src='http://s0.wp.com/latex.php?latex=%7BBC%28X+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{BC(X &#92;rightarrow {&#92;mathbb C})}' title='{BC(X &#92;rightarrow {&#92;mathbb C})}' class='latex' /> and <img src='http://s0.wp.com/latex.php?latex=%7BC%28%5Cbeta+X+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C(&#92;beta X &#92;rightarrow {&#92;mathbb C})}' title='{C(&#92;beta X &#92;rightarrow {&#92;mathbb C})}' class='latex' />.</p>
<p>We&#8217;ve simultaneously shown points one and two.</p>
<p><strong> Bullet Point Three </strong></p>
<p>Let <img src='http://s0.wp.com/latex.php?latex=%7B%5Coverline%7BX%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;overline{X}}' title='{&#92;overline{X}}' class='latex' /> be a compactification of <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />. Consider the map <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota}' title='{&#92;iota}' class='latex' /> that takes a function <img src='http://s0.wp.com/latex.php?latex=%7Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f}' title='{f}' class='latex' /> in <img src='http://s0.wp.com/latex.php?latex=%7BC%28%5Coverline%7BX%7D+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C(&#92;overline{X} &#92;rightarrow {&#92;mathbb C})}' title='{C(&#92;overline{X} &#92;rightarrow {&#92;mathbb C})}' class='latex' /> and returns the function <img src='http://s0.wp.com/latex.php?latex=%7Bf%7C_X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f|_X}' title='{f|_X}' class='latex' />. From the previous bullet point, <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota}' title='{&#92;iota}' class='latex' /> is an injective homomorphism from the commutative unital <img src='http://s0.wp.com/latex.php?latex=%7BC%5E%2A%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C^*}' title='{C^*}' class='latex' />-algebra <img src='http://s0.wp.com/latex.php?latex=%7BC%28%5Coverline%7BX%7D+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C(&#92;overline{X} &#92;rightarrow {&#92;mathbb C})}' title='{C(&#92;overline{X} &#92;rightarrow {&#92;mathbb C})}' class='latex' /> to the commutative unital <img src='http://s0.wp.com/latex.php?latex=%7BC%5E%2A%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C^*}' title='{C^*}' class='latex' />-algebra <img src='http://s0.wp.com/latex.php?latex=%7BBC%28X+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{BC(X &#92;rightarrow {&#92;mathbb C})}' title='{BC(X &#92;rightarrow {&#92;mathbb C})}' class='latex' /> that preserves the anti-linear transformation on both <img src='http://s0.wp.com/latex.php?latex=%7BC%5E%2A%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C^*}' title='{C^*}' class='latex' />-algebras. We don&#8217;t have to change anything in our argument in the previous part to show that this <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota}' title='{&#92;iota}' class='latex' /> is also an isometry. Now to show that the image of <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota}' title='{&#92;iota}' class='latex' /> contains <img src='http://s0.wp.com/latex.php?latex=%7B%7B%5Cmathbb+C%7D+%5Coplus+C_0%28X+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{{&#92;mathbb C} &#92;oplus C_0(X &#92;rightarrow {&#92;mathbb C})}' title='{{&#92;mathbb C} &#92;oplus C_0(X &#92;rightarrow {&#92;mathbb C})}' class='latex' />.</p>
<p>Let <img src='http://s0.wp.com/latex.php?latex=%7Bf+%5Cin+C_0%28X+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f &#92;in C_0(X &#92;rightarrow {&#92;mathbb C})}' title='{f &#92;in C_0(X &#92;rightarrow {&#92;mathbb C})}' class='latex' />. So given an <img src='http://s0.wp.com/latex.php?latex=%7B%5Cepsilon+%3E+0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;epsilon &gt; 0}' title='{&#92;epsilon &gt; 0}' class='latex' />, there exists a compact set <img src='http://s0.wp.com/latex.php?latex=%7BK+%5Csubset+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{K &#92;subset X}' title='{K &#92;subset X}' class='latex' /> such that <img src='http://s0.wp.com/latex.php?latex=%7B%7Cf%28x%29%7C+%5Cleq+%5Cepsilon%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{|f(x)| &#92;leq &#92;epsilon}' title='{|f(x)| &#92;leq &#92;epsilon}' class='latex' /> when <img src='http://s0.wp.com/latex.php?latex=%7Bx+%5Cin+K%5Ec%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x &#92;in K^c}' title='{x &#92;in K^c}' class='latex' />. Consider the function <img src='http://s0.wp.com/latex.php?latex=%7B%5Ctilde%7Bf%7D%3A+%5Coverline%7BX%7D+%5Crightarrow+%7B%5Cmathbb+C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;tilde{f}: &#92;overline{X} &#92;rightarrow {&#92;mathbb C}}' title='{&#92;tilde{f}: &#92;overline{X} &#92;rightarrow {&#92;mathbb C}}' class='latex' /> where <img src='http://s0.wp.com/latex.php?latex=%7B%5Ctilde%7Bf%7D%7C_X%3Df%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;tilde{f}|_X=f}' title='{&#92;tilde{f}|_X=f}' class='latex' /> and <img src='http://s0.wp.com/latex.php?latex=%7B%5Ctilde%7Bf%7D%3D0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;tilde{f}=0}' title='{&#92;tilde{f}=0}' class='latex' /> on <img src='http://s0.wp.com/latex.php?latex=%7B%5Coverline%7BX%7D-X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;overline{X}-X}' title='{&#92;overline{X}-X}' class='latex' />. Let <img src='http://s0.wp.com/latex.php?latex=%7BU%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U}' title='{U}' class='latex' /> be open in <img src='http://s0.wp.com/latex.php?latex=%7B%5B0%2C1%5D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{[0,1]}' title='{[0,1]}' class='latex' />. If <img src='http://s0.wp.com/latex.php?latex=%7B0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{0}' title='{0}' class='latex' /> isn&#8217;t in <img src='http://s0.wp.com/latex.php?latex=%7BU%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U}' title='{U}' class='latex' />, then <img src='http://s0.wp.com/latex.php?latex=%7B%5Ctilde%7Bf%7D%5E%7B-1%7D%28U%29%3Df%5E%7B-1%7D%28U%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;tilde{f}^{-1}(U)=f^{-1}(U)}' title='{&#92;tilde{f}^{-1}(U)=f^{-1}(U)}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7Bf%5E%7B-1%7D%28U%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f^{-1}(U)}' title='{f^{-1}(U)}' class='latex' /> is open relative to <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />, and <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' /> is open relative to <img src='http://s0.wp.com/latex.php?latex=%7B%5Coverline%7BX%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;overline{X}}' title='{&#92;overline{X}}' class='latex' />, and thus <img src='http://s0.wp.com/latex.php?latex=%7Bf%5E%7B-1%7D%28U%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f^{-1}(U)}' title='{f^{-1}(U)}' class='latex' /> is open relative to <img src='http://s0.wp.com/latex.php?latex=%7B%5Coverline%7BX%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;overline{X}}' title='{&#92;overline{X}}' class='latex' />. Now if <img src='http://s0.wp.com/latex.php?latex=%7B0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{0}' title='{0}' class='latex' /> is in <img src='http://s0.wp.com/latex.php?latex=%7BU%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U}' title='{U}' class='latex' />, consider <img src='http://s0.wp.com/latex.php?latex=%7B%5Ctilde%7Bf%7D%5E%7B-1%7D%28U%29%3Df%5E%7B-1%7D%28U%29+%5Ccup+%28%5Coverline%7BX%7D-X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;tilde{f}^{-1}(U)=f^{-1}(U) &#92;cup (&#92;overline{X}-X)}' title='{&#92;tilde{f}^{-1}(U)=f^{-1}(U) &#92;cup (&#92;overline{X}-X)}' class='latex' />. Let <img src='http://s0.wp.com/latex.php?latex=%7Bx+%5Cin+f%5E%7B-1%7D%28U%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x &#92;in f^{-1}(U)}' title='{x &#92;in f^{-1}(U)}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7Bf%5E%7B-1%7D%28U%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{f^{-1}(U)}' title='{f^{-1}(U)}' class='latex' /> is open relative to <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />, and therefore is open relative to <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7Bx%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x}' title='{x}' class='latex' /> is an interior point. Suppose <img src='http://s0.wp.com/latex.php?latex=%7Bx+%5Cin+%5Coverline%7BX%7D-X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x &#92;in &#92;overline{X}-X}' title='{x &#92;in &#92;overline{X}-X}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7B%5Ctilde%7Bf%7D%28x%29%3D0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;tilde{f}(x)=0}' title='{&#92;tilde{f}(x)=0}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7BU%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{U}' title='{U}' class='latex' /> is an open set in <img src='http://s0.wp.com/latex.php?latex=%7B%5B0%2C1%5D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{[0,1]}' title='{[0,1]}' class='latex' /> that contains <img src='http://s0.wp.com/latex.php?latex=%7B0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{0}' title='{0}' class='latex' />. Therefore there exists an <img src='http://s0.wp.com/latex.php?latex=%7B%5Cepsilon+%3E+0%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;epsilon &gt; 0}' title='{&#92;epsilon &gt; 0}' class='latex' /> such that <img src='http://s0.wp.com/latex.php?latex=%7B%5B0%2C2%5Cepsilon%29+%5Csubset+U%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{[0,2&#92;epsilon) &#92;subset U}' title='{[0,2&#92;epsilon) &#92;subset U}' class='latex' />, then <img src='http://s0.wp.com/latex.php?latex=%7B%5B0%2C%5Cepsilon%5D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{[0,&#92;epsilon]}' title='{[0,&#92;epsilon]}' class='latex' />. There exists a compact set <img src='http://s0.wp.com/latex.php?latex=%7BK+%5Csubset+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{K &#92;subset X}' title='{K &#92;subset X}' class='latex' /> such that <img src='http://s0.wp.com/latex.php?latex=%7B%7Cf%28y%29%7C%5Cleq+%5Cepsilon%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{|f(y)|&#92;leq &#92;epsilon}' title='{|f(y)|&#92;leq &#92;epsilon}' class='latex' /> for all <img src='http://s0.wp.com/latex.php?latex=%7By+%5Cin+X+%5Cbackslash+K%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{y &#92;in X &#92;backslash K}' title='{y &#92;in X &#92;backslash K}' class='latex' />. Now <img src='http://s0.wp.com/latex.php?latex=%7BK%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{K}' title='{K}' class='latex' /> is compact relative to <img src='http://s0.wp.com/latex.php?latex=%7B%5Coverline%7BX%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;overline{X}}' title='{&#92;overline{X}}' class='latex' />, and <img src='http://s0.wp.com/latex.php?latex=%7B%7Cf%28y%29%7C%5Cleq+%5Cepsilon%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{|f(y)|&#92;leq &#92;epsilon}' title='{|f(y)|&#92;leq &#92;epsilon}' class='latex' /> for all <img src='http://s0.wp.com/latex.php?latex=%7By+%5Cin+%5Coverline%7BX%7D+%5Cbackslash+K%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{y &#92;in &#92;overline{X} &#92;backslash K}' title='{y &#92;in &#92;overline{X} &#92;backslash K}' class='latex' />. Therefore <img src='http://s0.wp.com/latex.php?latex=%7B%5Coverline%7BX%7D+%5Cbackslash+K+%5Csubset+%5Ctilde%7Bf%7D%5E%7B-1%7D%28U%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;overline{X} &#92;backslash K &#92;subset &#92;tilde{f}^{-1}(U)}' title='{&#92;overline{X} &#92;backslash K &#92;subset &#92;tilde{f}^{-1}(U)}' class='latex' />. We&#8217;ve found an open neighborhood around <img src='http://s0.wp.com/latex.php?latex=%7Bx%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x}' title='{x}' class='latex' /> that lies in <img src='http://s0.wp.com/latex.php?latex=%7B%5Ctilde%7Bf%7D%5E%7B-1%7D%28U%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;tilde{f}^{-1}(U)}' title='{&#92;tilde{f}^{-1}(U)}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7Bx%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{x}' title='{x}' class='latex' /> is an interior point. Therefore, <img src='http://s0.wp.com/latex.php?latex=%7B%5Ctilde%7Bf%7D%5E%7B-1%7D%28U%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;tilde{f}^{-1}(U)}' title='{&#92;tilde{f}^{-1}(U)}' class='latex' /> is open. <img src='http://s0.wp.com/latex.php?latex=%7B%5Ctilde%7Bf%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;tilde{f}}' title='{&#92;tilde{f}}' class='latex' /> is a continuous function from <img src='http://s0.wp.com/latex.php?latex=%7B%5Coverline%7BX%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;overline{X}}' title='{&#92;overline{X}}' class='latex' /> to <img src='http://s0.wp.com/latex.php?latex=%7B%7B%5Cmathbb+C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{{&#92;mathbb C}}' title='{{&#92;mathbb C}}' class='latex' />.</p>
<p>Therefore <img src='http://s0.wp.com/latex.php?latex=%7BC_0%28X+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C_0(X &#92;rightarrow {&#92;mathbb C})}' title='{C_0(X &#92;rightarrow {&#92;mathbb C})}' class='latex' /> is in the image of <img src='http://s0.wp.com/latex.php?latex=%7BC%28%5Coverline%7BX%7D+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C(&#92;overline{X} &#92;rightarrow {&#92;mathbb C})}' title='{C(&#92;overline{X} &#92;rightarrow {&#92;mathbb C})}' class='latex' /> under <img src='http://s0.wp.com/latex.php?latex=%7B%5Ciota%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;iota}' title='{&#92;iota}' class='latex' />. Let <img src='http://s0.wp.com/latex.php?latex=%7B1%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{1}' title='{1}' class='latex' /> denote the constant function <img src='http://s0.wp.com/latex.php?latex=%7B1%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{1}' title='{1}' class='latex' />, and let <img src='http://s0.wp.com/latex.php?latex=%7Bc%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{c}' title='{c}' class='latex' /> lie in <img src='http://s0.wp.com/latex.php?latex=%7B%7B%5Cmathbb+C%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{{&#92;mathbb C}}' title='{{&#92;mathbb C}}' class='latex' />. Now let <img src='http://s0.wp.com/latex.php?latex=%7Bc1%2Bf+%5Cin+%7B%5Cmathbb+C%7D+%5Coplus+C_0%28X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{c1+f &#92;in {&#92;mathbb C} &#92;oplus C_0(X)}' title='{c1+f &#92;in {&#92;mathbb C} &#92;oplus C_0(X)}' class='latex' />. There exists a <img src='http://s0.wp.com/latex.php?latex=%7B%5Ctilde%7Bf%7D+%5Cin+C%28%5Coverline%7BX%7D+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;tilde{f} &#92;in C(&#92;overline{X} &#92;rightarrow {&#92;mathbb C})}' title='{&#92;tilde{f} &#92;in C(&#92;overline{X} &#92;rightarrow {&#92;mathbb C})}' class='latex' /> such that <img src='http://s0.wp.com/latex.php?latex=%7B%5Ctilde%7Bf%7D%7C_X%3Df%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;tilde{f}|_X=f}' title='{&#92;tilde{f}|_X=f}' class='latex' />. Then <img src='http://s0.wp.com/latex.php?latex=%7B%28c1%2B%5Ctilde%7Bf%7D%29%7C_X%3Dc1%7C_X%2B%5Ctilde%7Bf%7D%7C_X%3Dc1%2Bf%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{(c1+&#92;tilde{f})|_X=c1|_X+&#92;tilde{f}|_X=c1+f}' title='{(c1+&#92;tilde{f})|_X=c1|_X+&#92;tilde{f}|_X=c1+f}' class='latex' />. <img src='http://s0.wp.com/latex.php?latex=%7B%7B%5Cmathbb+C%7D+%5Coplus+C_0%28X+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{{&#92;mathbb C} &#92;oplus C_0(X &#92;rightarrow {&#92;mathbb C})}' title='{{&#92;mathbb C} &#92;oplus C_0(X &#92;rightarrow {&#92;mathbb C})}' class='latex' /> lies in the image of <img src='http://s0.wp.com/latex.php?latex=%7BC%28%5Coverline%7BX%7D+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C(&#92;overline{X} &#92;rightarrow {&#92;mathbb C})}' title='{C(&#92;overline{X} &#92;rightarrow {&#92;mathbb C})}' class='latex' />.</p>
<p><strong> Exercise 6 </strong></p>
<p>Let <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' /> be the Stone-Cech compactification of <img src='http://s0.wp.com/latex.php?latex=%7BX%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{X}' title='{X}' class='latex' />. The proof that <img src='http://s0.wp.com/latex.php?latex=%7BBC%28X+%5Crightarrow+%7B%5Cmathbb+R%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{BC(X &#92;rightarrow {&#92;mathbb R})}' title='{BC(X &#92;rightarrow {&#92;mathbb R})}' class='latex' /> is isomorphic to <img src='http://s0.wp.com/latex.php?latex=%7BC%28%5Cbeta+X+%5Crightarrow+%7B%5Cmathbb+R%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C(&#92;beta X &#92;rightarrow {&#92;mathbb R})}' title='{C(&#92;beta X &#92;rightarrow {&#92;mathbb R})}' class='latex' /> as Banach spaces was our proof that <img src='http://s0.wp.com/latex.php?latex=%7BBC%28X+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{BC(X &#92;rightarrow {&#92;mathbb C})}' title='{BC(X &#92;rightarrow {&#92;mathbb C})}' class='latex' /> is isomorphic as a <img src='http://s0.wp.com/latex.php?latex=%7BC%5E%2A%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C^*}' title='{C^*}' class='latex' />-algebra to <img src='http://s0.wp.com/latex.php?latex=%7BC%28%5Cbeta+X+%5Crightarrow+%7B%5Cmathbb+C%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C(&#92;beta X &#92;rightarrow {&#92;mathbb C})}' title='{C(&#92;beta X &#92;rightarrow {&#92;mathbb C})}' class='latex' /> with some steps omitted. Therefore <img src='http://s0.wp.com/latex.php?latex=%7BBC%28X+%5Crightarrow+%7B%5Cmathbb+R%7D%29%5E%2A%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{BC(X &#92;rightarrow {&#92;mathbb R})^*}' title='{BC(X &#92;rightarrow {&#92;mathbb R})^*}' class='latex' /> is isomorphic to <img src='http://s0.wp.com/latex.php?latex=%7BC%28%5Cbeta+X+%5Crightarrow+%7B%5Cmathbb+R%7D%29%5E%2A%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C(&#92;beta X &#92;rightarrow {&#92;mathbb R})^*}' title='{C(&#92;beta X &#92;rightarrow {&#92;mathbb R})^*}' class='latex' />. Since <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' /> is a compact Hausdorff space, <img src='http://s0.wp.com/latex.php?latex=%7BC%28%5Cbeta+X+%5Crightarrow+%7B%5Cmathbb+R%7D%29%5E%2A%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{C(&#92;beta X &#92;rightarrow {&#92;mathbb R})^*}' title='{C(&#92;beta X &#92;rightarrow {&#92;mathbb R})^*}' class='latex' /> is isomorphic to the space <img src='http://s0.wp.com/latex.php?latex=%7BM%28+%5Cbeta+X%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{M( &#92;beta X)}' title='{M( &#92;beta X)}' class='latex' /> of real signed Radon measures on <img src='http://s0.wp.com/latex.php?latex=%7B%5Cbeta+X%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;beta X}' title='{&#92;beta X}' class='latex' /> according to the Reisz Representation Theorem. The complex case is identical.</p>
<p>Any function on <img src='http://s0.wp.com/latex.php?latex=%7B%7B%5Cmathbb+N%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{{&#92;mathbb N}}' title='{{&#92;mathbb N}}' class='latex' /> is continuous, therefore <img src='http://s0.wp.com/latex.php?latex=%7B%5Cell%5E%5Cinfty%28%7B%5Cmathbb+N%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;ell^&#92;infty({&#92;mathbb N})}' title='{&#92;ell^&#92;infty({&#92;mathbb N})}' class='latex' /> is the space of bounded continuous function on <img src='http://s0.wp.com/latex.php?latex=%7B%7B%5Cmathbb+N%7D%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{{&#92;mathbb N}}' title='{{&#92;mathbb N}}' class='latex' />. Therefore <img src='http://s0.wp.com/latex.php?latex=%7B%5Cell%5E%5Cinfty%28%7B%5Cmathbb+N%7D%29+%5Cequiv+M%28%5Cbeta+%7B%5Cmathbb+N%7D%29%7D&amp;bg=ffffff&amp;fg=000000&amp;s=0' alt='{&#92;ell^&#92;infty({&#92;mathbb N}) &#92;equiv M(&#92;beta {&#92;mathbb N})}' title='{&#92;ell^&#92;infty({&#92;mathbb N}) &#92;equiv M(&#92;beta {&#92;mathbb N})}' class='latex' />.</p>
<br />  <a rel="nofollow" href="http://feeds.wordpress.com/1.0/gocomments/maxbaroi.wordpress.com/84/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/comments/maxbaroi.wordpress.com/84/" /></a> <a rel="nofollow" href="http://feeds.wordpress.com/1.0/godelicious/maxbaroi.wordpress.com/84/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/delicious/maxbaroi.wordpress.com/84/" /></a> <a rel="nofollow" href="http://feeds.wordpress.com/1.0/gofacebook/maxbaroi.wordpress.com/84/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/facebook/maxbaroi.wordpress.com/84/" /></a> <a rel="nofollow" href="http://feeds.wordpress.com/1.0/gotwitter/maxbaroi.wordpress.com/84/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/twitter/maxbaroi.wordpress.com/84/" /></a> <a rel="nofollow" href="http://feeds.wordpress.com/1.0/gostumble/maxbaroi.wordpress.com/84/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/stumble/maxbaroi.wordpress.com/84/" /></a> <a rel="nofollow" href="http://feeds.wordpress.com/1.0/godigg/maxbaroi.wordpress.com/84/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/digg/maxbaroi.wordpress.com/84/" /></a> <a rel="nofollow" href="http://feeds.wordpress.com/1.0/goreddit/maxbaroi.wordpress.com/84/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/reddit/maxbaroi.wordpress.com/84/" /></a> <img alt="" border="0" src="http://stats.wordpress.com/b.gif?host=maxbaroi.wordpress.com&amp;blog=6922221&amp;post=84&amp;subd=maxbaroi&amp;ref=&amp;feed=1" width="1" height="1" />]]></content:encoded>
			<wfw:commentRss>http://maxbaroi.wordpress.com/2009/04/05/245b-notes-13-compactification-and-metrisation/feed/</wfw:commentRss>
		<slash:comments>0</slash:comments>
	
		<media:content url="http://0.gravatar.com/avatar/40e1819f1064072b650dfcaca1d604f6?s=96&#38;d=identicon&#38;r=G" medium="image">
			<media:title type="html">maxbaroi</media:title>
		</media:content>
	</item>
		<item>
		<title>Marjoe</title>
		<link>http://maxbaroi.wordpress.com/2009/03/20/marjoe/</link>
		<comments>http://maxbaroi.wordpress.com/2009/03/20/marjoe/#comments</comments>
		<pubDate>Fri, 20 Mar 2009 08:19:33 +0000</pubDate>
		<dc:creator>maxbaroi</dc:creator>
				<category><![CDATA[Art Stuff]]></category>

		<guid isPermaLink="false">http://maxbaroi.wordpress.com/?p=73</guid>
		<description><![CDATA[I just saw a documentary called Marjoe that&#8217;s available in full on youtube. It&#8217;s about a man that used to be (and actually still was at the time of filming) a Pentecostal minister. Our unfortunately name hero/sort-of-villian became a minister at the age of 4. His parents paraded him around as a novelty act until [...]<img alt="" border="0" src="http://stats.wordpress.com/b.gif?host=maxbaroi.wordpress.com&amp;blog=6922221&amp;post=73&amp;subd=maxbaroi&amp;ref=&amp;feed=1" width="1" height="1" />]]></description>
			<content:encoded><![CDATA[<p>I just saw a documentary called <a title="Marjoe" href="http://www.youtube.com/watch?v=fKln1sQXvmo&amp;feature=PlayList&amp;p=6DC324C340D6F3F2&amp;index=18" target="_blank">Marjoe</a> that&#8217;s available in full on youtube. It&#8217;s about a man that used to be (and actually still was at the time of filming) a Pentecostal minister. Our unfortunately name hero/sort-of-villian became a minister at the age of 4. His parents paraded him around as a novelty act until he got sick of it as a teenager. He went back to preaching as an adult, because, well, if you had a get rich quick scheme you&#8217;ve spent a lifetime perfecting, wouldn&#8217;t you go out and do it? I was almost tempted to write, &#8220;this time, purely as a cynic looking for some quick cash,&#8221; but he plainly admits that he never believed what he was preaching. He seems more upset that his parents didn&#8217;t give him any cut of the cash than ruining his childhood. They did teach him how to make a living.</p>
<p>The movie&#8217;s not an attack on Pentecostalism. Marjoe even gives them an honest endorsement as the Christian curch he&#8217;d belong to if he had to choose one. They never mention in the movie any doctronial isssues on which the Pentecost church differs from other churches. Sure there&#8217;s the shaking on the floor, the healing through prayer, and other shows, but the club handshakes don&#8217;t tell you a club&#8217;s beliefs and values.</p>
<p>I like Marjoe, it&#8217;s hard not to like him. He&#8217;s smart, charaismatic, and has a certain power. I must admit that I have bias towards people like that because I&#8217;m the polar opposite. Those people are strange to me. I don&#8217;t understand how they tick, from where they get that power. So I&#8217;m always interested when something takes a closer look at that type of person.</p>
<p>This movie is a behind the curtain look of a rouse and its con man. He explains some fake miracles to his camera crew, but that&#8217;s only a fraction of what he does. The con isn&#8217;t his parlor tricks but him. He has passion and energy. He speaks with conviction and power. He&#8217;s a skilled entertainer, and even when he&#8217;s not singing his voice has a musical quality to it. When you watch him preach there is no crack in the performance. There is no keyhole through which we see that jaded cynic that must be half-laughing half-crying at the power his performance has over his audience.</p>
<p>This isn&#8217;t harmless fun. He even recognizes the bad he&#8217;s doing. I&#8217;ve read accounts of James Randi doing cold-readings (for those of you that haven&#8217;t taken an interest in the battle between skepticism and psuedo-science/paranormal-activity, a cold-reading is the name of the parlor trick off of which John Edwards has based his entire), and he puts on a good show. But at the end, he always reveals that it was just that, a show. And at no points did he ever collect money from the people he was tricking. I don&#8217;t know if this was intenttional but the symbolism smacks you in the face. There is a scene where Marjoe&#8217;s audience line up and puts money in a waste bin. He realizes what he&#8217;s doing is wrong, he doens&#8217;t feel guilty enough to not take his victims&#8217; money,  but the desire to end his sham is the impetus for the creation of the movie.</p>
<p>There isn&#8217;t really too much straight criticism found in the movie. The strongest piece would be a zoom-in on an elaborate broche pinned to a woman that asks the people in the pews to donate money to the cash-straped church, while reassuring them that the church doesn&#8217;t spend foolishly. Even when Marjoe&#8217;s father is presented, all Marjoe says is that the only thing they can really talk about is his father&#8217;s back-yard.</p>
<p>Probably the best scene is one towards the end that features Marjoe, his girl friend, and a dog. At this point he&#8217;s stated how he&#8217;s tired of his double-life, the lies, and he wants a new life with the girl he loves. It&#8217;s a huanting scene because he&#8217;s at full-force in it. It shows the incredible talent and personality that&#8217;s essentialy been wasted on a single trick. He&#8217;s not giving up just a rouse, but what&#8217;s been his life. It&#8217;s an increidbly interesting movie if only because it is the atonement of a fascianting person.</p>
<p>But I have to admit, if there is one child prohet I&#8217;m going to follow, it would be this <a href="http://www.youtube.com/watch?v=_V4K7FepKw4" target="_blank">one</a>. Sorry Marjoe.</p>
<br />  <a rel="nofollow" href="http://feeds.wordpress.com/1.0/gocomments/maxbaroi.wordpress.com/73/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/comments/maxbaroi.wordpress.com/73/" /></a> <a rel="nofollow" href="http://feeds.wordpress.com/1.0/godelicious/maxbaroi.wordpress.com/73/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/delicious/maxbaroi.wordpress.com/73/" /></a> <a rel="nofollow" href="http://feeds.wordpress.com/1.0/gofacebook/maxbaroi.wordpress.com/73/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/facebook/maxbaroi.wordpress.com/73/" /></a> <a rel="nofollow" href="http://feeds.wordpress.com/1.0/gotwitter/maxbaroi.wordpress.com/73/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/twitter/maxbaroi.wordpress.com/73/" /></a> <a rel="nofollow" href="http://feeds.wordpress.com/1.0/gostumble/maxbaroi.wordpress.com/73/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/stumble/maxbaroi.wordpress.com/73/" /></a> <a rel="nofollow" href="http://feeds.wordpress.com/1.0/godigg/maxbaroi.wordpress.com/73/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/digg/maxbaroi.wordpress.com/73/" /></a> <a rel="nofollow" href="http://feeds.wordpress.com/1.0/goreddit/maxbaroi.wordpress.com/73/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/reddit/maxbaroi.wordpress.com/73/" /></a> <img alt="" border="0" src="http://stats.wordpress.com/b.gif?host=maxbaroi.wordpress.com&amp;blog=6922221&amp;post=73&amp;subd=maxbaroi&amp;ref=&amp;feed=1" width="1" height="1" />]]></content:encoded>
			<wfw:commentRss>http://maxbaroi.wordpress.com/2009/03/20/marjoe/feed/</wfw:commentRss>
		<slash:comments>0</slash:comments>
	
		<media:content url="http://0.gravatar.com/avatar/40e1819f1064072b650dfcaca1d604f6?s=96&#38;d=identicon&#38;r=G" medium="image">
			<media:title type="html">maxbaroi</media:title>
		</media:content>
	</item>
		<item>
		<title>Introductory Remarks</title>
		<link>http://maxbaroi.wordpress.com/2009/03/12/introductory-remarks/</link>
		<comments>http://maxbaroi.wordpress.com/2009/03/12/introductory-remarks/#comments</comments>
		<pubDate>Thu, 12 Mar 2009 03:01:45 +0000</pubDate>
		<dc:creator>maxbaroi</dc:creator>
				<category><![CDATA[Uncategorized]]></category>

		<guid isPermaLink="false">http://maxbaroi.wordpress.com/?p=5</guid>
		<description><![CDATA[This is the first in what I hope to be many posts. The immediate goal of this blog is to collect and post solutions to the various exercises that Professor Tao has posted in his various course notes. Ideally, this blog would have been created in early January when his latest course (Math 245B) began. [...]<img alt="" border="0" src="http://stats.wordpress.com/b.gif?host=maxbaroi.wordpress.com&amp;blog=6922221&amp;post=5&amp;subd=maxbaroi&amp;ref=&amp;feed=1" width="1" height="1" />]]></description>
			<content:encoded><![CDATA[<p>
This is the first in what I hope to be many posts. The immediate goal of this blog is to collect and post solutions to the various exercises that Professor Tao has posted in his various course notes. Ideally, this blog would have been created in early January when his latest course (Math 245B) began. Right now, his Math 245B exercises are a way to work out the kinks to posting and maintaining a blog, so that when Professor Tao starts his 245C course (in two to three weeks) this blog will be ready for the onslaught of exercises he has in store.</p>
<p>
There is a huge backlog of problems. I plan on initially just having thirteen essentially blank posts (one for each of his notes), with each post just consisting of the exercise numbers, and I&#8217;ll fill the space next to each of those numbers with the corresponding proof as I get around to typing one up or posting a submitted answer. This way my posts are ordered the same way as Professor Tao&#8217;s. </p>
<p>
I&#8217;ll post the problem lists soon, and I will fill in what I can when I have time, but as I said before, I do hope to receive help. If this blog is a sort of answering of a challenge from Professor Tao&#8217;s blog, then this blog is at a serious disadvantage in thus duel. As previously stated, there is a tremendous backlog of problems, intrinsically it takes less time read a problem than it is to answer it, and I am much more of a mere mortal than Professor Tao. </p>
<p>
So here we go.</p>
<br />  <a rel="nofollow" href="http://feeds.wordpress.com/1.0/gocomments/maxbaroi.wordpress.com/5/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/comments/maxbaroi.wordpress.com/5/" /></a> <a rel="nofollow" href="http://feeds.wordpress.com/1.0/godelicious/maxbaroi.wordpress.com/5/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/delicious/maxbaroi.wordpress.com/5/" /></a> <a rel="nofollow" href="http://feeds.wordpress.com/1.0/gofacebook/maxbaroi.wordpress.com/5/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/facebook/maxbaroi.wordpress.com/5/" /></a> <a rel="nofollow" href="http://feeds.wordpress.com/1.0/gotwitter/maxbaroi.wordpress.com/5/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/twitter/maxbaroi.wordpress.com/5/" /></a> <a rel="nofollow" href="http://feeds.wordpress.com/1.0/gostumble/maxbaroi.wordpress.com/5/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/stumble/maxbaroi.wordpress.com/5/" /></a> <a rel="nofollow" href="http://feeds.wordpress.com/1.0/godigg/maxbaroi.wordpress.com/5/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/digg/maxbaroi.wordpress.com/5/" /></a> <a rel="nofollow" href="http://feeds.wordpress.com/1.0/goreddit/maxbaroi.wordpress.com/5/"><img alt="" border="0" src="http://feeds.wordpress.com/1.0/reddit/maxbaroi.wordpress.com/5/" /></a> <img alt="" border="0" src="http://stats.wordpress.com/b.gif?host=maxbaroi.wordpress.com&amp;blog=6922221&amp;post=5&amp;subd=maxbaroi&amp;ref=&amp;feed=1" width="1" height="1" />]]></content:encoded>
			<wfw:commentRss>http://maxbaroi.wordpress.com/2009/03/12/introductory-remarks/feed/</wfw:commentRss>
		<slash:comments>0</slash:comments>
	
		<media:content url="http://0.gravatar.com/avatar/40e1819f1064072b650dfcaca1d604f6?s=96&#38;d=identicon&#38;r=G" medium="image">
			<media:title type="html">maxbaroi</media:title>
		</media:content>
	</item>
	</channel>
</rss>
