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

<b>let </b><font color="Maroon">X1</font> be    <a href="hidden.html#M1">set</a> ;<br/><b>let </b><font color="Maroon">X2</font> be    <a href="hidden.html#M1">set</a> ;<br/><b>let </b><font color="Maroon">X3</font> be    <a href="hidden.html#M1">set</a> ;<br/><b>let </b><font color="Maroon">X4</font> be    <a href="hidden.html#M1">set</a> ;<br/>







<a NAME="E1:2"/><i><font color="Green">E19</font></i>: 
( <font color="Maroon">X1</font> <a href="hidden.html#R2">in</a> <span class="p1"><a href="enumset1.html#K2">{</a><span class="default"><font color="Maroon">X1</font>,<font color="Maroon">X2</font>,<font color="Maroon">X3</font>,<font color="Maroon">X4</font></span><a href="enumset1.html#K2">}</a></span> &amp; <font color="Maroon">X2</font> <a href="hidden.html#R2">in</a> <span class="p1"><a href="enumset1.html#K2">{</a><span class="default"><font color="Maroon">X1</font>,<font color="Maroon">X2</font>,<font color="Maroon">X3</font>,<font color="Maroon">X4</font></span><a href="enumset1.html#K2">}</a></span> &amp; <font color="Maroon">X3</font> <a href="hidden.html#R2">in</a> <span class="p1"><a href="enumset1.html#K2">{</a><span class="default"><font color="Maroon">X1</font>,<font color="Maroon">X2</font>,<font color="Maroon">X3</font>,<font color="Maroon">X4</font></span><a href="enumset1.html#K2">}</a></span> &amp; <font color="Maroon">X4</font> <a href="hidden.html#R2">in</a> <span class="p1"><a href="enumset1.html#K2">{</a><span class="default"><font color="Maroon">X1</font>,<font color="Maroon">X2</font>,<font color="Maroon">X3</font>,<font color="Maroon">X4</font></span><a href="enumset1.html#K2">}</a></span> )
 
<b>by </b><i><a class="ref" href="enumset1.html#D2">ENUMSET1:def 2</a></i>;<br/>
<b>then consider </b><font color="Maroon">T</font> being    <a href="hidden.html#M1">set</a> <b> such that </b><br/><a NAME="E3:2"/><i><font color="Green">E21</font></i>: 
<font color="Maroon">T</font> <a href="hidden.html#R2">in</a> <span class="p1"><a href="enumset1.html#K2">{</a><span class="default"><font color="Maroon">X1</font>,<font color="Maroon">X2</font>,<font color="Maroon">X3</font>,<font color="Maroon">X4</font></span><a href="enumset1.html#K2">}</a></span>
 <b>and </b><br/><a NAME="E4:2"/><i><font color="Green">E22</font></i>: 
for <font color="Olive">x</font> being   <a href="hidden.html#M1">set</a>   holds <br/>(  not <font color="Olive">x</font> <a href="hidden.html#R2">in</a> <span class="p1"><a href="enumset1.html#K2">{</a><span class="default"><font color="Maroon">X1</font>,<font color="Maroon">X2</font>,<font color="Maroon">X3</font>,<font color="Maroon">X4</font></span><a href="enumset1.html#K2">}</a></span> or  not <font color="Olive">x</font> <a href="hidden.html#R2">in</a> <font color="Maroon">T</font> )
 <b>by </b><i><a class="ref" href="tarski.html#T7">TARSKI:7</a></i>;<br/>
<a NAME="E5:2"/>
( <font color="Maroon">T</font> <a href="hidden.html#R1">=</a> <font color="Maroon">X1</font> or <font color="Maroon">T</font> <a href="hidden.html#R1">=</a> <font color="Maroon">X2</font> or <font color="Maroon">T</font> <a href="hidden.html#R1">=</a> <font color="Maroon">X3</font> or <font color="Maroon">T</font> <a href="hidden.html#R1">=</a> <font color="Maroon">X4</font> )
 
<b>by </b><i>, <a class="ref" href="enumset1.html#D2">ENUMSET1:def 2</a></i>;<br/>
<b>hence </b><a NAME="E6:2"/>
(  not <font color="Maroon">X1</font> <a href="hidden.html#R2">in</a> <font color="Maroon">X2</font> or  not <font color="Maroon">X2</font> <a href="hidden.html#R2">in</a> <font color="Maroon">X3</font> or  not <font color="Maroon">X3</font> <a href="hidden.html#R2">in</a> <font color="Maroon">X4</font> or  not <font color="Maroon">X4</font> <a href="hidden.html#R2">in</a> <font color="Maroon">X1</font> )
 <b>by </b><i>, </i>;<br/>


</div>
