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<b>let </b><font color="Maroon">c<sub>1</sub></font> be   <a href="nat_1.html#NM1">Nat</a>;<br/>

<a NAME="E1:78"/><i><font color="Green">E63</font></i>: 
<span class="p1">(<span class="default"><a href="pepin.html#K5" target="_self">Fermat</a> <font color="Maroon">c<sub>1</sub></font></span>)</span> <a href="xcmplx_0.html#K6">-</a> 1 <a href="hidden.html#R1">=</a> <span class="p1">(<span class="default"><a href="pepin.html#K5" target="_self">Fermat</a> <font color="Maroon">c<sub>1</sub></font></span>)</span> <a href="binarith.html#K5">-'</a> 1
 
<b>by </b><i><a class="ref" href="binarith.html#D3">BINARITH:def 3</a></i>;<br/>
<a NAME="E2:78"/>
<span class="p1">(<span class="default"><span class="p2">(<span class="default"><a href="pepin.html#K5" target="_self">Fermat</a> <font color="Maroon">c<sub>1</sub></font></span>)</span> <a href="binarith.html#K5">-'</a> 1</span>)</span> <a href="nat_1.html#K4">mod</a> 2 <a href="hidden.html#R1">=</a> 0
 
<b>by </b><i><a class="txt" href="pepin.html#E82"><i><font color="Green">Lemma59</font></i></a></i>;<br/>
<a NAME="E3:78"/><b>then </b>
<span class="p1">(<span class="default"><a href="pepin.html#K5" target="_self">Fermat</a> <font color="Maroon">c<sub>1</sub></font></span>)</span> <a href="binarith.html#K5">-'</a> 1 is <a href="abian.html#V1">even</a>
 
<b>by </b><i><a class="ref" href="nat_2.html#T23">NAT_2:23</a></i>;<br/>
<b>hence </b><a NAME="E4:78"/>
not  <a href="pepin.html#K5" target="_self">Fermat</a> <font color="Maroon">c<sub>1</sub></font> is <a href="abian.html#V1">even</a>
 <b>by </b><i><a class="txt" href="pepin.html#E1:78"><i><font color="Green">E63</font></i></a>, <a class="ref" href="pepin.html#T16" target="_self">Th16</a></i>;<br/>


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