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<b>let </b><font color="Maroon">D</font> be  non <a href="xboole_0.html#V1">empty</a>  <a href="hidden.html#M1">set</a> ;<br/><b>let </b><font color="Maroon">i</font> be   <a href="nat_1.html#NM1">Nat</a>;<br/><b>let </b><font color="Maroon">z</font> be    <a href="finseq_2.html#M2" target="_self">Element</a> of <font color="Maroon">i</font> <a href="finseq_2.html#K4" target="_self">-tuples_on</a> <font color="Maroon">D</font>;<br/>





<a NAME="E1:109"/>
<font color="Maroon">z</font> <a href="hidden.html#R2">in</a> <span class="p1">{<span class="default"> <font color="Olive">p'</font> where <font color="Olive">p'</font> is    <a href="finseq_2.html#M2" target="_self">Element</a> of <font color="Maroon">D</font> <a href="finseq_2.html#K3" target="_self">*</a>  :  <a href="finseq_1.html#K3">len</a> <font color="Olive">p'</font> <a href="hidden.html#R1">=</a> <font color="Maroon">i</font> </span>}</span> 
 
;<br/>
<a NAME="E2:109"/><b>then </b>
 ex <font color="Olive">p'</font> being   <a href="finseq_2.html#M2" target="_self">Element</a> of <font color="Maroon">D</font> <a href="finseq_2.html#K3" target="_self">*</a>  st <br/>( <font color="Olive">p'</font> <a href="hidden.html#R1">=</a> <font color="Maroon">z</font> &amp;  <a href="finseq_1.html#K3">len</a> <font color="Olive">p'</font> <a href="hidden.html#R1">=</a> <font color="Maroon">i</font> )
 
;<br/>
<b>hence </b><a NAME="E3:109"/>
 <a href="finseq_1.html#K3">len</a> <font color="Maroon">z</font> <a href="hidden.html#R1">=</a> <font color="Maroon">i</font>
 ;<br/>


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