<?xml version="1.0"?>
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<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/><b>let </b><font color="Maroon">Y1</font> be    <a href="hidden.html#M1">set</a> ;<br/><b>let </b><font color="Maroon">Y2</font> be    <a href="hidden.html#M1">set</a> ;<br/><b>let </b><font color="Maroon">Y3</font> be    <a href="hidden.html#M1">set</a> ;<br/><b>let </b><font color="Maroon">Y4</font> be    <a href="hidden.html#M1">set</a> ;<br/>















<a NAME="E1:54"/><i><font color="Green">E39</font></i>: 
<span class="p1"><a href="zfmisc_1.html#K4">[:</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="zfmisc_1.html#K4">:]</a></span> <a href="hidden.html#R1">=</a> <span class="p1"><a href="zfmisc_1.html#K2">[:</a><span class="default"><span class="p2"><a href="zfmisc_1.html#K3">[:</a><span class="default"><font color="Maroon">X1</font>,<font color="Maroon">X2</font>,<font color="Maroon">X3</font></span><a href="zfmisc_1.html#K3">:]</a></span>,<font color="Maroon">X4</font></span><a href="zfmisc_1.html#K2">:]</a></span>
 
<b>by </b><i><a class="ref" href="zfmisc_1.html#D4">ZFMISC_1:def 4</a></i>;<br/>
<b>assume </b><a NAME="E2:54"/><i><font color="Green">E40</font></i>: 
( <font color="Maroon">X1</font> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a>  <a href="xboole_0.html#K1">{}</a>  &amp; <font color="Maroon">X2</font> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a>  <a href="xboole_0.html#K1">{}</a>  &amp; <font color="Maroon">X3</font> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a>  <a href="xboole_0.html#K1">{}</a>  )
 ;<br/>

<a NAME="E3:54"/><b>then </b><i><font color="Green">E43</font></i>: 
<span class="p1"><a href="zfmisc_1.html#K3">[:</a><span class="default"><font color="Maroon">X1</font>,<font color="Maroon">X2</font>,<font color="Maroon">X3</font></span><a href="zfmisc_1.html#K3">:]</a></span> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a>  <a href="xboole_0.html#K1">{}</a> 
 
<b>by </b><i/>;<br/>
<b>assume </b><a NAME="E4:54"/><i><font color="Green">E44</font></i>: 
<font color="Maroon">X4</font> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a>  <a href="xboole_0.html#K1">{}</a> 
 ;<br/>

<b>assume </b><a NAME="E5:54"/>
<span class="p1"><a href="zfmisc_1.html#K4">[:</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="zfmisc_1.html#K4">:]</a></span> <a href="hidden.html#R1">=</a> <span class="p1"><a href="zfmisc_1.html#K4">[:</a><span class="default"><font color="Maroon">Y1</font>,<font color="Maroon">Y2</font>,<font color="Maroon">Y3</font>,<font color="Maroon">Y4</font></span><a href="zfmisc_1.html#K4">:]</a></span>
 ;<br/>

<a NAME="E6:54"/><b>then </b>
<span class="p1"><a href="zfmisc_1.html#K2">[:</a><span class="default"><span class="p2"><a href="zfmisc_1.html#K3">[:</a><span class="default"><font color="Maroon">X1</font>,<font color="Maroon">X2</font>,<font color="Maroon">X3</font></span><a href="zfmisc_1.html#K3">:]</a></span>,<font color="Maroon">X4</font></span><a href="zfmisc_1.html#K2">:]</a></span> <a href="hidden.html#R1">=</a> <span class="p1"><a href="zfmisc_1.html#K2">[:</a><span class="default"><span class="p2"><a href="zfmisc_1.html#K3">[:</a><span class="default"><font color="Maroon">Y1</font>,<font color="Maroon">Y2</font>,<font color="Maroon">Y3</font></span><a href="zfmisc_1.html#K3">:]</a></span>,<font color="Maroon">Y4</font></span><a href="zfmisc_1.html#K2">:]</a></span>
 
<b>by </b><i>, <a class="ref" href="zfmisc_1.html#D4">ZFMISC_1:def 4</a></i>;<br/>
<a NAME="E7:54"/><b>then </b>
( <span class="p1"><a href="zfmisc_1.html#K3">[:</a><span class="default"><font color="Maroon">X1</font>,<font color="Maroon">X2</font>,<font color="Maroon">X3</font></span><a href="zfmisc_1.html#K3">:]</a></span> <a href="hidden.html#R1">=</a> <span class="p1"><a href="zfmisc_1.html#K3">[:</a><span class="default"><font color="Maroon">Y1</font>,<font color="Maroon">Y2</font>,<font color="Maroon">Y3</font></span><a href="zfmisc_1.html#K3">:]</a></span> &amp; <font color="Maroon">X4</font> <a href="hidden.html#R1">=</a> <font color="Maroon">Y4</font> )
 
<b>by </b><i>, <a class="ref" href="mcart_1.html#T1" target="_self">Th1</a>, <a class="ref" href="zfmisc_1.html#T134">ZFMISC_1:134</a></i>;<br/>
<b>hence </b><a NAME="E8:54"/>
( <font color="Maroon">X1</font> <a href="hidden.html#R1">=</a> <font color="Maroon">Y1</font> &amp; <font color="Maroon">X2</font> <a href="hidden.html#R1">=</a> <font color="Maroon">Y2</font> &amp; <font color="Maroon">X3</font> <a href="hidden.html#R1">=</a> <font color="Maroon">Y3</font> &amp; <font color="Maroon">X4</font> <a href="hidden.html#R1">=</a> <font color="Maroon">Y4</font> )
 <b>by </b><i>, </i>;<br/>


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