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	<id>https://calculus.subwiki.org/w/index.php?action=history&amp;feed=atom&amp;title=Continuous_functions_form_a_unital_algebra</id>
	<title>Continuous functions form a unital algebra - Revision history</title>
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	<updated>2026-04-27T07:16:52Z</updated>
	<subtitle>Revision history for this page on the wiki</subtitle>
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	<entry>
		<id>https://calculus.subwiki.org/w/index.php?title=Continuous_functions_form_a_unital_algebra&amp;diff=460&amp;oldid=prev</id>
		<title>Vipul at 15:54, 16 October 2011</title>
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		<updated>2011-10-16T15:54:51Z</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 15:54, 16 October 2011&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-l6&quot;&gt;Line 6:&lt;/td&gt;
&lt;td colspan=&quot;2&quot; class=&quot;diff-lineno&quot;&gt;Line 6:&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;* &amp;#039;&amp;#039;&amp;#039;Additive closure&amp;#039;&amp;#039;&amp;#039;: If &amp;lt;math&amp;gt;f,g&amp;lt;/math&amp;gt; are functions defined in open intervals containing &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt; and both of them are [[fact about::continuous function|continuous]] at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;, then the [[fact about::pointwise sum of functions|pointwise sum]] &amp;lt;math&amp;gt;f + g&amp;lt;/math&amp;gt; is continuous at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;.&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;* &amp;#039;&amp;#039;&amp;#039;Additive closure&amp;#039;&amp;#039;&amp;#039;: If &amp;lt;math&amp;gt;f,g&amp;lt;/math&amp;gt; are functions defined in open intervals containing &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt; and both of them are [[fact about::continuous function|continuous]] at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;, then the [[fact about::pointwise sum of functions|pointwise sum]] &amp;lt;math&amp;gt;f + g&amp;lt;/math&amp;gt; is continuous at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;.&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&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: #ffe49c; vertical-align: top; white-space: pre-wrap;&quot;&gt;&lt;div&gt;* &#039;&#039;&#039;Scalar &lt;del style=&quot;font-weight: bold; text-decoration: none;&quot;&gt;multiplies&lt;/del&gt;&#039;&#039;&#039;: If &amp;lt;math&amp;gt;f&amp;lt;/math&amp;gt; is defined in an open interval containing &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt; and is continuous at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;, and &amp;lt;math&amp;gt;\lambda&amp;lt;/math&amp;gt; is a real number, then &amp;lt;math&amp;gt;\lambda f&amp;lt;/math&amp;gt; is continuous at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;.&lt;/div&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;* &#039;&#039;&#039;Scalar &lt;ins style=&quot;font-weight: bold; text-decoration: none;&quot;&gt;multiples&lt;/ins&gt;&#039;&#039;&#039;: If &amp;lt;math&amp;gt;f&amp;lt;/math&amp;gt; is defined in an open interval containing &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt; and is continuous at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;, and &amp;lt;math&amp;gt;\lambda&amp;lt;/math&amp;gt; is a real number, then &amp;lt;math&amp;gt;\lambda f&amp;lt;/math&amp;gt; is continuous at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;.&lt;/div&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;* &amp;#039;&amp;#039;&amp;#039;Multiplicative identity&amp;#039;&amp;#039;&amp;#039;: The [[constant function]] that sends everything to &amp;lt;math&amp;gt;1&amp;lt;/math&amp;gt; is continuous at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;.&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;* &amp;#039;&amp;#039;&amp;#039;Multiplicative identity&amp;#039;&amp;#039;&amp;#039;: The [[constant function]] that sends everything to &amp;lt;math&amp;gt;1&amp;lt;/math&amp;gt; is continuous at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;.&lt;/div&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;* &amp;#039;&amp;#039;&amp;#039;Multiplicative closure&amp;#039;&amp;#039;&amp;#039;: If &amp;lt;math&amp;gt;f,g&amp;lt;/math&amp;gt; are functions defined in open intervals containing &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt; and both of them are [[fact about::continuous function|continuous]] at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;, then the [[fact about::pointwise product of functions|pointwise product]] &amp;lt;math&amp;gt;f \cdot g&amp;lt;/math&amp;gt; is continuous at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;.&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;* &amp;#039;&amp;#039;&amp;#039;Multiplicative closure&amp;#039;&amp;#039;&amp;#039;: If &amp;lt;math&amp;gt;f,g&amp;lt;/math&amp;gt; are functions defined in open intervals containing &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt; and both of them are [[fact about::continuous function|continuous]] at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;, then the [[fact about::pointwise product of functions|pointwise product]] &amp;lt;math&amp;gt;f \cdot g&amp;lt;/math&amp;gt; is continuous at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;.&lt;/div&gt;&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-l17&quot;&gt;Line 17:&lt;/td&gt;
&lt;td colspan=&quot;2&quot; class=&quot;diff-lineno&quot;&gt;Line 17:&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;* &amp;#039;&amp;#039;&amp;#039;Additive closure&amp;#039;&amp;#039;&amp;#039;: If &amp;lt;math&amp;gt;f,g&amp;lt;/math&amp;gt; are functions defined and continuous in open intervals containing &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;, then the [[fact about::pointwise sum of functions|pointwise sum]] &amp;lt;math&amp;gt;f + g&amp;lt;/math&amp;gt; is continuous at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;.&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;* &amp;#039;&amp;#039;&amp;#039;Additive closure&amp;#039;&amp;#039;&amp;#039;: If &amp;lt;math&amp;gt;f,g&amp;lt;/math&amp;gt; are functions defined and continuous in open intervals containing &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;, then the [[fact about::pointwise sum of functions|pointwise sum]] &amp;lt;math&amp;gt;f + g&amp;lt;/math&amp;gt; is continuous at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;.&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&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: #ffe49c; vertical-align: top; white-space: pre-wrap;&quot;&gt;&lt;div&gt;* &#039;&#039;&#039;Scalar &lt;del style=&quot;font-weight: bold; text-decoration: none;&quot;&gt;multiplies&lt;/del&gt;&#039;&#039;&#039;: If &amp;lt;math&amp;gt;f&amp;lt;/math&amp;gt; is defined and continuous in an open interval containing &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;&amp;gt;, and &amp;lt;math&amp;gt;\lambda&amp;lt;/math&amp;gt; is a real number, then &amp;lt;math&amp;gt;\lambda f&amp;lt;/math&amp;gt; is continuous at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;.&lt;/div&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;* &#039;&#039;&#039;Scalar &lt;ins style=&quot;font-weight: bold; text-decoration: none;&quot;&gt;multiples&lt;/ins&gt;&#039;&#039;&#039;: If &amp;lt;math&amp;gt;f&amp;lt;/math&amp;gt; is defined and continuous in an open interval containing &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;&amp;gt;, and &amp;lt;math&amp;gt;\lambda&amp;lt;/math&amp;gt; is a real number, then &amp;lt;math&amp;gt;\lambda f&amp;lt;/math&amp;gt; is continuous at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;.&lt;/div&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;* &amp;#039;&amp;#039;&amp;#039;Multiplicative identity&amp;#039;&amp;#039;&amp;#039;: The [[constant function]] that sends everything to &amp;lt;math&amp;gt;1&amp;lt;/math&amp;gt; is continuous in an open interval containing &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;.&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;* &amp;#039;&amp;#039;&amp;#039;Multiplicative identity&amp;#039;&amp;#039;&amp;#039;: The [[constant function]] that sends everything to &amp;lt;math&amp;gt;1&amp;lt;/math&amp;gt; is continuous in an open interval containing &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;.&lt;/div&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;* &amp;#039;&amp;#039;&amp;#039;Multiplicative closure&amp;#039;&amp;#039;&amp;#039;: If &amp;lt;math&amp;gt;f,g&amp;lt;/math&amp;gt; are functions defined and continuous in open intervals containing &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;, then the [[fact about::pointwise product of functions|pointwise product]] &amp;lt;math&amp;gt;f \cdot g&amp;lt;/math&amp;gt; is continuous at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;.&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;* &amp;#039;&amp;#039;&amp;#039;Multiplicative closure&amp;#039;&amp;#039;&amp;#039;: If &amp;lt;math&amp;gt;f,g&amp;lt;/math&amp;gt; are functions defined and continuous in open intervals containing &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;, then the [[fact about::pointwise product of functions|pointwise product]] &amp;lt;math&amp;gt;f \cdot g&amp;lt;/math&amp;gt; is continuous at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;.&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;/table&gt;</summary>
		<author><name>Vipul</name></author>
	</entry>
	<entry>
		<id>https://calculus.subwiki.org/w/index.php?title=Continuous_functions_form_a_unital_algebra&amp;diff=459&amp;oldid=prev</id>
		<title>Vipul at 15:54, 16 October 2011</title>
		<link rel="alternate" type="text/html" href="https://calculus.subwiki.org/w/index.php?title=Continuous_functions_form_a_unital_algebra&amp;diff=459&amp;oldid=prev"/>
		<updated>2011-10-16T15:54:23Z</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 15:54, 16 October 2011&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-l5&quot;&gt;Line 5:&lt;/td&gt;
&lt;td colspan=&quot;2&quot; class=&quot;diff-lineno&quot;&gt;Line 5:&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;Suppose &amp;lt;math&amp;gt;c \in \R&amp;lt;/math&amp;gt;. Then, the following are true:&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;Suppose &amp;lt;math&amp;gt;c \in \R&amp;lt;/math&amp;gt;. Then, the following are true:&lt;/div&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;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; 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: #ffe49c; vertical-align: top; white-space: pre-wrap;&quot;&gt;&lt;div&gt;* &#039;&#039;Additive closure&#039;&#039;: If &amp;lt;math&amp;gt;f,g&amp;lt;/math&amp;gt; are functions defined in open intervals containing &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt; and both of them are [[fact about::continuous function|continuous]] at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;, then the [[fact about::pointwise sum of functions|pointwise sum]] &amp;lt;math&amp;gt;f + g&amp;lt;/math&amp;gt; is continuous at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;.&lt;/div&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;&#039;&lt;/ins&gt;&#039;&#039;Additive closure&lt;ins style=&quot;font-weight: bold; text-decoration: none;&quot;&gt;&#039;&lt;/ins&gt;&#039;&#039;: If &amp;lt;math&amp;gt;f,g&amp;lt;/math&amp;gt; are functions defined in open intervals containing &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt; and both of them are [[fact about::continuous function|continuous]] at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;, then the [[fact about::pointwise sum of functions|pointwise sum]] &amp;lt;math&amp;gt;f + g&amp;lt;/math&amp;gt; is continuous at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;.&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&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: #ffe49c; vertical-align: top; white-space: pre-wrap;&quot;&gt;&lt;div&gt;* &#039;&#039;Scalar multiplies&#039;&#039;: If &amp;lt;math&amp;gt;f&amp;lt;/math&amp;gt; is defined in an open interval containing &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt; and is continuous at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;, and &amp;lt;math&amp;gt;\lambda&amp;lt;/math&amp;gt; is a real number, then &amp;lt;math&amp;gt;\lambda f&amp;lt;/math&amp;gt; is continuous at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;.&lt;/div&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;&#039;&lt;/ins&gt;&#039;&#039;Scalar multiplies&lt;ins style=&quot;font-weight: bold; text-decoration: none;&quot;&gt;&#039;&lt;/ins&gt;&#039;&#039;: If &amp;lt;math&amp;gt;f&amp;lt;/math&amp;gt; is defined in an open interval containing &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt; and is continuous at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;, and &amp;lt;math&amp;gt;\lambda&amp;lt;/math&amp;gt; is a real number, then &amp;lt;math&amp;gt;\lambda f&amp;lt;/math&amp;gt; is continuous at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;.&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&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: #ffe49c; vertical-align: top; white-space: pre-wrap;&quot;&gt;&lt;div&gt;* &#039;&#039;Multiplicative closure&#039;&#039;: If &amp;lt;math&amp;gt;f,g&amp;lt;/math&amp;gt; are functions defined in open intervals containing &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt; and both of them are [[fact about::continuous function|continuous]] at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;, then the [[fact about::pointwise product of functions|pointwise product]] &amp;lt;math&amp;gt;f \cdot g&amp;lt;/math&amp;gt; is continuous at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;.&lt;/div&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;&#039;&#039;&#039;Multiplicative identity&#039;&#039;&#039;: The [[constant function]] that sends everything to &amp;lt;math&amp;gt;1&amp;lt;/math&amp;gt; is continuous at &amp;lt;math&amp;gt;c&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;* &#039;&lt;/ins&gt;&#039;&#039;Multiplicative closure&lt;ins style=&quot;font-weight: bold; text-decoration: none;&quot;&gt;&#039;&lt;/ins&gt;&#039;&#039;: If &amp;lt;math&amp;gt;f,g&amp;lt;/math&amp;gt; are functions defined in open intervals containing &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt; and both of them are [[fact about::continuous function|continuous]] at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;, then the [[fact about::pointwise product of functions|pointwise product]] &amp;lt;math&amp;gt;f \cdot g&amp;lt;/math&amp;gt; is continuous at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;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;/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;There is a technical way of forming a [[unital algebra]] (a vector space endowed with an identity and a compatible multiplication) from the set of continuous functions at the point &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;, once we identify (as being the same) any two functoins that agree on an open interval containing &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;. This approach is called &#039;&#039;taking the germ of the function&#039;&#039;.&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;/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;===Continuity around a point version===&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;/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;Suppose &amp;lt;math&amp;gt;c \in \R&amp;lt;/math&amp;gt;. Then, the following are true:&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;/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;* &#039;&#039;&#039;Additive closure&#039;&#039;&#039;: If &amp;lt;math&amp;gt;f,g&amp;lt;/math&amp;gt; are functions defined and continuous in open intervals containing &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;, then the [[fact about::pointwise sum of functions|pointwise sum]] &amp;lt;math&amp;gt;f + g&amp;lt;/math&amp;gt; is continuous at &amp;lt;math&amp;gt;c&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;* &#039;&#039;&#039;Scalar multiplies&#039;&#039;&#039;: If &amp;lt;math&amp;gt;f&amp;lt;/math&amp;gt; is defined and continuous in an open interval containing &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;&amp;gt;, and &amp;lt;math&amp;gt;\lambda&amp;lt;/math&amp;gt; is a real number, then &amp;lt;math&amp;gt;\lambda f&amp;lt;/math&amp;gt; is continuous at &amp;lt;math&amp;gt;c&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;* &#039;&#039;&#039;Multiplicative identity&#039;&#039;&#039;: The [[constant function]] that sends everything to &amp;lt;math&amp;gt;1&amp;lt;/math&amp;gt; is continuous in an open interval containing &amp;lt;math&amp;gt;c&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;* &#039;&#039;&#039;Multiplicative closure&#039;&#039;&#039;: If &amp;lt;math&amp;gt;f,g&amp;lt;/math&amp;gt; are functions defined and continuous in open intervals containing &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;, then the [[fact about::pointwise product of functions|pointwise product]] &amp;lt;math&amp;gt;f \cdot g&amp;lt;/math&amp;gt; is continuous at &amp;lt;math&amp;gt;c&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;/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;There is a technical way of forming a [[unital algebra]] (a vector space endowed with an identity and a compatible multiplication) from the set of continuous functions at the point &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;, once we identify (as being the same) any two functoins that agree on an open interval containing &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;. This approach is called &#039;&#039;taking the germ of the function&#039;&#039;.&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;/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;===Continuity on an interval version===&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;/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;Suppose &amp;lt;math&amp;gt;I&amp;lt;/math&amp;gt; is an [[interval]] (possibly open, closed, or infinite from the left side and possibly open, closed, or infinite from the right side -- so it could be of the form &amp;lt;math&amp;gt;[a,b],[a,b),(a,b),(a,b],(-\infty,b),(-\infty,b],(a,\infty),[a,\infty),(-\infty,\infty)&amp;lt;/math&amp;gt;). A [[fact about::continuous function]] on &amp;lt;math&amp;gt;I&amp;lt;/math&amp;gt; is a function on &amp;lt;math&amp;gt;I&amp;lt;/math&amp;gt; that is continuous at all points on the &#039;&#039;interior&#039;&#039; of &amp;lt;math&amp;gt;I&amp;lt;/math&amp;gt; and has the appropriate one-sided continuity at the boundary points (if they exist).&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;/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 continuous functions on &amp;lt;math&amp;gt;I&amp;lt;/math&amp;gt; form a [[real vector space]], in the sense that the following hold:&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;/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;* &#039;&#039;&#039;Additive&#039;&#039;&#039;: A sum of continuous functions is continuous: If &amp;lt;math&amp;gt;f,g&amp;lt;/math&amp;gt; are both continuous functions on &amp;lt;math&amp;gt;I&amp;lt;/math&amp;gt;, so is the [[pointwise sum of functions]] &amp;lt;math&amp;gt;f + g&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;* &#039;&#039;&#039;Scalar multiples&#039;&#039;&#039;: If &amp;lt;math&amp;gt;\lambda \in \R&amp;lt;/math&amp;gt; and &amp;lt;math&amp;gt;f&amp;lt;/math&amp;gt; is a continuous function on &amp;lt;math&amp;gt;I&amp;lt;/math&amp;gt;, then &amp;lt;math&amp;gt;\lambda f&amp;lt;/math&amp;gt; is also a continuous function on &amp;lt;math&amp;gt;I&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;* &#039;&#039;Multiplicative identity&#039;&#039;&#039;: The constant function sending everything to 1 is a continuous function on &amp;lt;math&amp;gt;I&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;* &#039;&#039;&#039;Multiplicative closure&#039;&#039;&#039;: A product of continuous functions is continuous: If &amp;lt;math&amp;gt;f,g&amp;lt;/math&amp;gt; are both continuous functions on &amp;lt;math&amp;gt;I&amp;lt;/math&amp;gt;, so is the [[pointwise product of functions]] &amp;lt;math&amp;gt;f \cdot g&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;/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;==Facts used==&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;/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;# [[uses::Continuous functions form a vector space]]: This takes care of the addition and scalar multiples aspects&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;# [[uses::Limit is multiplicative]]: This takes care of multiplicative closure&lt;/ins&gt;&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;/table&gt;</summary>
		<author><name>Vipul</name></author>
	</entry>
	<entry>
		<id>https://calculus.subwiki.org/w/index.php?title=Continuous_functions_form_a_unital_algebra&amp;diff=454&amp;oldid=prev</id>
		<title>Vipul: Created page with &quot;==Statement==  ===Continuity at a point version===  Suppose &lt;math&gt;c \in \R&lt;/math&gt;. Then, the following are true:  * &#039;&#039;Additive closure&#039;&#039;: If &lt;math&gt;f,g&lt;/math&gt; are functions define...&quot;</title>
		<link rel="alternate" type="text/html" href="https://calculus.subwiki.org/w/index.php?title=Continuous_functions_form_a_unital_algebra&amp;diff=454&amp;oldid=prev"/>
		<updated>2011-10-16T15:44:38Z</updated>

		<summary type="html">&lt;p&gt;Created page with &amp;quot;==Statement==  ===Continuity at a point version===  Suppose &amp;lt;math&amp;gt;c \in \R&amp;lt;/math&amp;gt;. Then, the following are true:  * &amp;#039;&amp;#039;Additive closure&amp;#039;&amp;#039;: If &amp;lt;math&amp;gt;f,g&amp;lt;/math&amp;gt; are functions define...&amp;quot;&lt;/p&gt;
&lt;p&gt;&lt;b&gt;New page&lt;/b&gt;&lt;/p&gt;&lt;div&gt;==Statement==&lt;br /&gt;
&lt;br /&gt;
===Continuity at a point version===&lt;br /&gt;
&lt;br /&gt;
Suppose &amp;lt;math&amp;gt;c \in \R&amp;lt;/math&amp;gt;. Then, the following are true:&lt;br /&gt;
&lt;br /&gt;
* &amp;#039;&amp;#039;Additive closure&amp;#039;&amp;#039;: If &amp;lt;math&amp;gt;f,g&amp;lt;/math&amp;gt; are functions defined in open intervals containing &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt; and both of them are [[fact about::continuous function|continuous]] at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;, then the [[fact about::pointwise sum of functions|pointwise sum]] &amp;lt;math&amp;gt;f + g&amp;lt;/math&amp;gt; is continuous at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;.&lt;br /&gt;
* &amp;#039;&amp;#039;Scalar multiplies&amp;#039;&amp;#039;: If &amp;lt;math&amp;gt;f&amp;lt;/math&amp;gt; is defined in an open interval containing &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt; and is continuous at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;, and &amp;lt;math&amp;gt;\lambda&amp;lt;/math&amp;gt; is a real number, then &amp;lt;math&amp;gt;\lambda f&amp;lt;/math&amp;gt; is continuous at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;.&lt;br /&gt;
* &amp;#039;&amp;#039;Multiplicative closure&amp;#039;&amp;#039;: If &amp;lt;math&amp;gt;f,g&amp;lt;/math&amp;gt; are functions defined in open intervals containing &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt; and both of them are [[fact about::continuous function|continuous]] at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;, then the [[fact about::pointwise product of functions|pointwise product]] &amp;lt;math&amp;gt;f \cdot g&amp;lt;/math&amp;gt; is continuous at &amp;lt;math&amp;gt;c&amp;lt;/math&amp;gt;.&lt;/div&gt;</summary>
		<author><name>Vipul</name></author>
	</entry>
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