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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/>

<b>thus </b><a NAME="E1:67"/>
2 <a href="nat_1.html#K2">*</a> <font color="Maroon">c<sub>1</sub></font> <a href="hidden.html#R2">in</a>  <a href="fib_num2.html#K3" target="_self">EvenNAT</a> 
 ;<br/>

<b>assume </b><a NAME="E2:67"/>
<span class="p1">(<span class="default">2 <a href="nat_1.html#K2">*</a> <font color="Maroon">c<sub>1</sub></font></span>)</span> <a href="nat_1.html#K1">+</a> 1 <a href="hidden.html#R2">in</a>  <a href="fib_num2.html#K3" target="_self">EvenNAT</a> 
 ;<br/>

<b>then consider </b><font color="Maroon">c<sub>2</sub></font> being   <a href="nat_1.html#NM1">Nat</a><b> such that </b><br/><a NAME="E4:67"/><i><font color="Green">E50</font></i>: 
<span class="p1">(<span class="default">2 <a href="nat_1.html#K2">*</a> <font color="Maroon">c<sub>1</sub></font></span>)</span> <a href="nat_1.html#K1">+</a> 1 <a href="hidden.html#R1">=</a> 2 <a href="nat_1.html#K2">*</a> <font color="Maroon">c<sub>2</sub></font>
 ;<br/>
<b>thus </b><a NAME="E5:67"/>
contradiction
 <b>by </b><i><a class="txt" href="fib_num2.html#E4:67"><i><font color="Green">E50</font></i></a></i>;<br/>


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