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<b>take </b>
1
;<br/>

<b>let </b><font color="Maroon">c<sub>1</sub></font> be   <a href="nat_1.html#NM1">Nat</a>; <i><font color="Red">:: according to </font></i><a class="ref" href="abian.html#D2" target="_self">ABIAN:def 2</a><br/>

<b>assume </b><a NAME="E1:5_2_1"/>
1 <a href="hidden.html#R1">=</a> 2 <a href="nat_1.html#K2">*</a> <font color="Maroon">c<sub>1</sub></font>
 ;<br/>

<b>hence </b><a NAME="E2:5_2_1"/>
contradiction
 <b>by </b><i><a class="ref" href="nat_1.html#T40">NAT_1:40</a></i>;<br/>


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