<?xml version="1.0"?>
<div class="add">

<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">X</font> be    <a href="hidden.html#M1">set</a> ;<br/><b>let </b><font color="Maroon">r</font> be    <a href="subset_1.html#M1">Element</a> of  <a href="margrel1.html#K3" target="_self">relations_on</a> <font color="Maroon">D</font>;<br/>





<b>assume </b><a NAME="E1:20"/><i><font color="Green">E23</font></i>: 
<font color="Maroon">X</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">r</font>
 ;<br/>

<a NAME="E2:20"/>
<font color="Maroon">X</font> <a href="hidden.html#R2">in</a>  <a href="margrel1.html#K3" target="_self">relations_on</a> <font color="Maroon">D</font>
 
<div><a class="txt" onclick="hs2(this)" href="javascript:()" title="20_1"><b>proof </b></a><div class="add">

<a NAME="E1:20_1"/>
<font color="Maroon">r</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">D</font> <a href="finseq_1.html#K13">*</a> 
 
<b>by </b><i/>;<br/>
<a NAME="E2:20_1"/><b>then </b><i><font color="Green">E36</font></i>: 
<font color="Maroon">X</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">D</font> <a href="finseq_1.html#K13">*</a> 
 
<b>by </b><i>, <a class="ref" href="xboole_1.html#T1">XBOOLE_1:1</a></i>;<br/>
<a NAME="E3:20_1"/>
for <font color="Olive">a</font>, <font color="Olive">b</font> being   <a href="finseq_1.html#M2">FinSequence</a> of <font color="Maroon">D</font>  st <font color="Olive">a</font> <a href="hidden.html#R2">in</a> <font color="Maroon">X</font> &amp; <font color="Olive">b</font> <a href="hidden.html#R2">in</a> <font color="Maroon">X</font> holds <br/> <a href="finseq_1.html#K3">len</a> <font color="Olive">a</font> <a href="hidden.html#R1">=</a>  <a href="finseq_1.html#K3">len</a> <font color="Olive">b</font>
 
<b>by </b><i>, </i>;<br/>
<b>hence </b><a NAME="E4:20_1"/>
<font color="Maroon">X</font> <a href="hidden.html#R2">in</a>  <a href="margrel1.html#K3" target="_self">relations_on</a> <font color="Maroon">D</font>
 <b>by </b><i>, </i>;<br/>


</div><b>end;</b></div>
<b>hence </b><a NAME="E3:20"/>
<font color="Maroon">X</font> is    <a href="subset_1.html#M1">Element</a> of  <a href="margrel1.html#K3" target="_self">relations_on</a> <font color="Maroon">D</font>
 ;<br/>


</div>
