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

<b>assume </b><a NAME="E1:11"/><i><font color="Green">E31</font></i>: 
0 <a href="xxreal_0.html#NR2" target="_self">&gt;=</a> <font color="Maroon">i</font> <a href="xcmplx_0.html#K2">+</a> 1
 ;<br/>

<a NAME="E2:11"/>
0 <a href="xxreal_0.html#R1">&lt;=</a> <font color="Maroon">i</font>
 
<b>by </b><i/>;<br/>
<a NAME="E3:11"/><b>then </b>
0 <a href="nat_1.html#K1" target="_self">+</a> 1 <a href="xxreal_0.html#R1">&lt;=</a> 0
 
<b>by </b><i>, <a class="ref" href="xreal_1.html#T9">XREAL_1:9</a></i>;<br/>
<b>hence </b><a NAME="E4:11"/>
contradiction
 ;<br/>


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