Check Wikipedia.&nbsp; Peirce law, law of excluded middle, double negation, ... they are all equivalent and it can be instructive to see how one can derive one from the other.<br><br><div><span class="gmail_quote">On 10/17/07, 
<b class="gmail_sendername">Tim Newsham</b> &lt;<a href="mailto:newsham@lava.net">newsham@lava.net</a>&gt; wrote:</span><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
&gt; Very clear tutorial indeed. But why isn&#39;t propCC shown as Pierce&#39;s<br>&gt; Law? And Excluded middle is proven on such basis.<br><br>Simply because I don&#39;t know that much about pierce&#39;s law.&nbsp;&nbsp;I&#39;ve<br>
seen it mentioned a few times, but I&#39;m not that familiar with it<br>yet and I haven&#39;t read a good treatment of it yet.&nbsp;&nbsp;Do you have<br>any pointers to something I could read?<br><br>&gt; Vitaliy.<br><br>Tim Newsham
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