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<b>let </b><font color="Maroon">n</font> be    <a href="subset_1.html#M1">Element</a> of  <a href="numbers.html#K5">NAT</a> ;<br/>

<b>assume </b><a NAME="E1:28"/>
<font color="Maroon">n</font> is <a href="abian.html#V1">even</a>
 ;<br/>

<a NAME="E2:28"/><b>then </b>
<font color="Maroon">n</font> <a href="nat_1.html#K6">mod</a> 2 <a href="hidden.html#R1">=</a> 0
 
<b>by </b><i><a class="ref" href="nat_2.html#T23">NAT_2:23</a></i>;<br/>
<b>then consider </b><font color="Maroon">k</font> being   <a href="nat_1.html#NM1">Nat</a><b> such that </b><br/><a NAME="E4:28"/><i><font color="Green">E44</font></i>: 
( <font color="Maroon">n</font> <a href="hidden.html#R1">=</a> <span class="p1">(<span class="default">2 <a href="xcmplx_0.html#K3">*</a> <font color="Maroon">k</font></span>)</span> <a href="xcmplx_0.html#K2">+</a> 0 &amp; 0 <a href="xxreal_0.html#NR3" target="_self">&lt;</a> 2 )
 <b>by </b><i><a class="ref" href="nat_1.html#D2">NAT_1:def 2</a></i>;<br/>
<span class="p1">(<span class="default"><font color="Maroon">n</font> <a href="nat_1.html#K1">+</a> 1</span>)</span> <a href="nat_1.html#K6">mod</a> 2 = 
1 <a href="nat_1.html#K6">mod</a> 2
<b>by </b><i>, <a class="ref" href="nat_1.html#T73">NAT_1:73</a></i>
<br/>.= 
1
<b>by </b><i><a class="ref" href="nat_1.html#T64">NAT_1:64</a></i>
;<br/>
<b>hence </b><a NAME="E6:28"/>
not <font color="Maroon">n</font> <a href="nat_1.html#K1">+</a> 1 is <a href="abian.html#V1">even</a>
 <b>by </b><i><a class="ref" href="nat_2.html#T24">NAT_2:24</a></i>;<br/>


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