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

<b>assume </b><b>that </b><br/><a NAME="E1:4_1_2"/><i><font color="Green">E61</font></i>: 
 <a href="zf_lang.html#K2">x.</a> <font color="Maroon">k</font> <a href="hidden.html#R1">=</a> <font color="Maroon">v1</font>
 <b>and </b><br/><a NAME="E2:4_1_2"/><i><font color="Green">E62</font></i>: 
 <a href="zf_lang.html#K2">x.</a> <font color="Maroon">k'</font> <a href="hidden.html#R1">=</a> <font color="Maroon">v1</font>
 ;<br/>

<a NAME="E3:4_1_2"/>
( 5 <a href="nat_1.html#K1">+</a> <font color="Maroon">k</font> <a href="hidden.html#R1">=</a> <font color="Maroon">v1</font> &amp; 5 <a href="nat_1.html#K1">+</a> <font color="Maroon">k'</font> <a href="hidden.html#R1">=</a> <font color="Maroon">v1</font> )
 
<b>by </b><i>, , <a class="ref" href="zf_lang.html#D2">ZF_LANG:def 2</a></i>;<br/>
<b>hence </b><a NAME="E4:4_1_2"/>
<font color="Maroon">k</font> <a href="hidden.html#R1">=</a> <font color="Maroon">k'</font>
 <b>by </b><i><a class="ref" href="xcmplx_1.html#T2">XCMPLX_1:2</a></i>;<br/>


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