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	<id>https://michaelnielsen.org/polymath/index.php?action=history&amp;feed=atom&amp;title=Corners</id>
	<title>Corners - Revision history</title>
	<link rel="self" type="application/atom+xml" href="https://michaelnielsen.org/polymath/index.php?action=history&amp;feed=atom&amp;title=Corners"/>
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	<updated>2026-07-29T16:05:00Z</updated>
	<subtitle>Revision history for this page on the wiki</subtitle>
	<generator>MediaWiki 1.42.3</generator>
	<entry>
		<id>https://michaelnielsen.org/polymath/index.php?title=Corners&amp;diff=709&amp;oldid=prev</id>
		<title>Jozsef at 01:17, 9 March 2009</title>
		<link rel="alternate" type="text/html" href="https://michaelnielsen.org/polymath/index.php?title=Corners&amp;diff=709&amp;oldid=prev"/>
		<updated>2009-03-09T01:17:29Z</updated>

		<summary type="html">&lt;p&gt;&lt;/p&gt;
&lt;table style=&quot;background-color: #fff; color: #202122;&quot; data-mw=&quot;interface&quot;&gt;
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				&lt;td colspan=&quot;2&quot; style=&quot;background-color: #fff; color: #202122; text-align: center;&quot;&gt;← Older revision&lt;/td&gt;
				&lt;td colspan=&quot;2&quot; style=&quot;background-color: #fff; color: #202122; text-align: center;&quot;&gt;Revision as of 18:17, 8 March 2009&lt;/td&gt;
				&lt;/tr&gt;&lt;tr&gt;&lt;td colspan=&quot;2&quot; class=&quot;diff-lineno&quot; id=&quot;mw-diff-left-l2&quot;&gt;Line 2:&lt;/td&gt;
&lt;td colspan=&quot;2&quot; class=&quot;diff-lineno&quot;&gt;Line 2:&lt;/td&gt;&lt;/tr&gt;
&lt;tr&gt;&lt;td class=&quot;diff-marker&quot;&gt;&lt;/td&gt;&lt;td style=&quot;background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;&quot;&gt;&lt;br&gt;&lt;/td&gt;&lt;td class=&quot;diff-marker&quot;&gt;&lt;/td&gt;&lt;td style=&quot;background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;&quot;&gt;&lt;br&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&gt;&lt;td class=&quot;diff-marker&quot;&gt;&lt;/td&gt;&lt;td style=&quot;background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;&quot;&gt;&lt;div&gt;The [[corners theorem]] asserts that for every &amp;lt;math&amp;gt;\delta&amp;gt;0&amp;lt;/math&amp;gt; there exists n such that every subset A of &amp;lt;math&amp;gt;[n]^2&amp;lt;/math&amp;gt; of density at least &amp;lt;math&amp;gt;\delta&amp;lt;/math&amp;gt; contains a corner.&lt;/div&gt;&lt;/td&gt;&lt;td class=&quot;diff-marker&quot;&gt;&lt;/td&gt;&lt;td style=&quot;background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;&quot;&gt;&lt;div&gt;The [[corners theorem]] asserts that for every &amp;lt;math&amp;gt;\delta&amp;gt;0&amp;lt;/math&amp;gt; there exists n such that every subset A of &amp;lt;math&amp;gt;[n]^2&amp;lt;/math&amp;gt; of density at least &amp;lt;math&amp;gt;\delta&amp;lt;/math&amp;gt; contains a corner.&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&gt;&lt;td colspan=&quot;2&quot; class=&quot;diff-side-deleted&quot;&gt;&lt;/td&gt;&lt;td class=&quot;diff-marker&quot; data-marker=&quot;+&quot;&gt;&lt;/td&gt;&lt;td style=&quot;color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;&quot;&gt;&lt;div&gt;&lt;ins style=&quot;font-weight: bold; text-decoration: none;&quot;&gt;&lt;/ins&gt;&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&gt;&lt;td colspan=&quot;2&quot; class=&quot;diff-side-deleted&quot;&gt;&lt;/td&gt;&lt;td class=&quot;diff-marker&quot; data-marker=&quot;+&quot;&gt;&lt;/td&gt;&lt;td style=&quot;color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;&quot;&gt;&lt;div&gt;&lt;ins style=&quot;font-weight: bold; text-decoration: none;&quot;&gt;In general, a corner is a subset of &amp;lt;math&amp;gt;[n]^m&amp;lt;/math&amp;gt; of the form &amp;lt;math&amp;gt;\{(x_1,x_2,\ldots , x_m),(x_1+d,x_2,\ldots , x_m),(x_1,x_2+d,\ldots , x_m),\ldots ,(x_1,x_2,\ldots , x_m+d)\}&amp;lt;/math&amp;gt; with &amp;lt;math&amp;gt;d\ne 0.&amp;lt;/math&amp;gt; &lt;/ins&gt;&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&gt;&lt;td colspan=&quot;2&quot; class=&quot;diff-side-deleted&quot;&gt;&lt;/td&gt;&lt;td class=&quot;diff-marker&quot; data-marker=&quot;+&quot;&gt;&lt;/td&gt;&lt;td style=&quot;color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;&quot;&gt;&lt;div&gt;&lt;ins style=&quot;font-weight: bold; text-decoration: none;&quot;&gt;&lt;/ins&gt;&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&gt;&lt;td colspan=&quot;2&quot; class=&quot;diff-side-deleted&quot;&gt;&lt;/td&gt;&lt;td class=&quot;diff-marker&quot; data-marker=&quot;+&quot;&gt;&lt;/td&gt;&lt;td style=&quot;color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;&quot;&gt;&lt;div&gt;&lt;ins style=&quot;font-weight: bold; text-decoration: none;&quot;&gt;The Multidimensional Szemeredi&#039;s theorem (proved by Furstenberg and Katznelson) asserts that for every real &amp;lt;math&amp;gt;\delta&amp;gt;0&amp;lt;/math&amp;gt; and integer &amp;lt;math&amp;gt;m&amp;gt;1&amp;lt;/math&amp;gt; there exists n such that every subset A of &amp;lt;math&amp;gt;[n]^m&amp;lt;/math&amp;gt; of density at least &amp;lt;math&amp;gt;\delta&amp;lt;/math&amp;gt; contains a corner.&lt;/ins&gt;&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
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		<author><name>Jozsef</name></author>
	</entry>
	<entry>
		<id>https://michaelnielsen.org/polymath/index.php?title=Corners&amp;diff=296&amp;oldid=prev</id>
		<title>Gowers: Created article</title>
		<link rel="alternate" type="text/html" href="https://michaelnielsen.org/polymath/index.php?title=Corners&amp;diff=296&amp;oldid=prev"/>
		<updated>2009-02-16T18:55:29Z</updated>

		<summary type="html">&lt;p&gt;Created article&lt;/p&gt;
&lt;p&gt;&lt;b&gt;New page&lt;/b&gt;&lt;/p&gt;&lt;div&gt;A &amp;#039;&amp;#039;corner&amp;#039;&amp;#039; is a subset of &amp;lt;math&amp;gt;[n]^2&amp;lt;/math&amp;gt; of the form &amp;lt;math&amp;gt;\{(x,y),(x+d,y),(x,y+d)\}&amp;lt;/math&amp;gt; with &amp;lt;math&amp;gt;d\ne 0.&amp;lt;/math&amp;gt; One often insists also that d should be positive.&lt;br /&gt;
&lt;br /&gt;
The [[corners theorem]] asserts that for every &amp;lt;math&amp;gt;\delta&amp;gt;0&amp;lt;/math&amp;gt; there exists n such that every subset A of &amp;lt;math&amp;gt;[n]^2&amp;lt;/math&amp;gt; of density at least &amp;lt;math&amp;gt;\delta&amp;lt;/math&amp;gt; contains a corner.&lt;/div&gt;</summary>
		<author><name>Gowers</name></author>
	</entry>
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