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<b>let </b><font color="Maroon">A</font> be  non <a href="xboole_0.html#V1">empty</a> <a href="finsub_1.html#V4">preBoolean</a>  <a href="hidden.html#M1">set</a> ;<br/><b>let </b><font color="Maroon">B</font> be  non <a href="xboole_0.html#V1">empty</a> <a href="finsub_1.html#V4">preBoolean</a>  <a href="hidden.html#M1">set</a> ;<br/><b>let </b><font color="Maroon">a</font> be    <a href="subset_1.html#M1">Element</a> of <span class="p1"><a href="zfmisc_1.html#K2">[:</a><span class="default"><font color="Maroon">A</font>,<font color="Maroon">B</font></span><a href="zfmisc_1.html#K2">:]</a></span>;<br/><b>let </b><font color="Maroon">b</font> be    <a href="subset_1.html#M1">Element</a> of <span class="p1"><a href="zfmisc_1.html#K2">[:</a><span class="default"><font color="Maroon">A</font>,<font color="Maroon">B</font></span><a href="zfmisc_1.html#K2">:]</a></span>;<br/><b>let </b><font color="Maroon">c</font> be    <a href="subset_1.html#M1">Element</a> of <span class="p1"><a href="zfmisc_1.html#K2">[:</a><span class="default"><font color="Maroon">A</font>,<font color="Maroon">B</font></span><a href="zfmisc_1.html#K2">:]</a></span>;<br/>









<div><a class="txt" onclick="hs2(this)" href="javascript:()" title="6_1"><b>now </b></a><div class="add"><b>thus </b><span class="p1">(<span class="default"><font color="Maroon">a</font> <a href="normform.html#K2" target="_self">/\</a> <span class="p2">(<span class="default"><font color="Maroon">b</font> <a href="normform.html#K1" target="_self">\/</a> <font color="Maroon">c</font></span>)</span></span>)</span> <a href="domain_1.html#K2">`1</a>  = 
<span class="p1">(<span class="default"><font color="Maroon">a</font> <a href="domain_1.html#K2">`1</a> </span>)</span> <a href="finsub_1.html#K3">/\</a> <span class="p1">(<span class="default"><span class="p2">(<span class="default"><font color="Maroon">b</font> <a href="normform.html#K1" target="_self">\/</a> <font color="Maroon">c</font></span>)</span> <a href="domain_1.html#K2">`1</a> </span>)</span>
<b>by </b><i/>
<br/>.= 
<span class="p1">(<span class="default"><font color="Maroon">a</font> <a href="domain_1.html#K2">`1</a> </span>)</span> <a href="finsub_1.html#K3">/\</a> <span class="p1">(<span class="default"><span class="p2">(<span class="default"><font color="Maroon">b</font> <a href="domain_1.html#K2">`1</a> </span>)</span> <a href="finsub_1.html#K1">\/</a> <span class="p2">(<span class="default"><font color="Maroon">c</font> <a href="domain_1.html#K2">`1</a> </span>)</span></span>)</span>
<b>by </b><i/>
<br/>.= 
<span class="p1">(<span class="default"><span class="p2">(<span class="default"><font color="Maroon">a</font> <a href="domain_1.html#K2">`1</a> </span>)</span> <a href="finsub_1.html#K3">/\</a> <span class="p2">(<span class="default"><font color="Maroon">b</font> <a href="domain_1.html#K2">`1</a> </span>)</span></span>)</span> <a href="finsub_1.html#K1">\/</a> <span class="p1">(<span class="default"><span class="p2">(<span class="default"><font color="Maroon">a</font> <a href="domain_1.html#K2">`1</a> </span>)</span> <a href="finsub_1.html#K3">/\</a> <span class="p2">(<span class="default"><font color="Maroon">c</font> <a href="domain_1.html#K2">`1</a> </span>)</span></span>)</span>
<b>by </b><i><a class="ref" href="xboole_1.html#T23">XBOOLE_1:23</a></i>
<br/>.= 
<span class="p1">(<span class="default"><span class="p2">(<span class="default"><font color="Maroon">a</font> <a href="domain_1.html#K2">`1</a> </span>)</span> <a href="finsub_1.html#K3">/\</a> <span class="p2">(<span class="default"><font color="Maroon">b</font> <a href="domain_1.html#K2">`1</a> </span>)</span></span>)</span> <a href="finsub_1.html#K1">\/</a> <span class="p1">(<span class="default"><span class="p2">(<span class="default"><font color="Maroon">a</font> <a href="normform.html#K2" target="_self">/\</a> <font color="Maroon">c</font></span>)</span> <a href="domain_1.html#K2">`1</a> </span>)</span>
<b>by </b><i/>
<br/>.= 
<span class="p1">(<span class="default"><span class="p2">(<span class="default"><font color="Maroon">a</font> <a href="normform.html#K2" target="_self">/\</a> <font color="Maroon">b</font></span>)</span> <a href="domain_1.html#K2">`1</a> </span>)</span> <a href="finsub_1.html#K1">\/</a> <span class="p1">(<span class="default"><span class="p2">(<span class="default"><font color="Maroon">a</font> <a href="normform.html#K2" target="_self">/\</a> <font color="Maroon">c</font></span>)</span> <a href="domain_1.html#K2">`1</a> </span>)</span>
<b>by </b><i/>
<br/>.= 
<span class="p1">(<span class="default"><span class="p2">(<span class="default"><font color="Maroon">a</font> <a href="normform.html#K2" target="_self">/\</a> <font color="Maroon">b</font></span>)</span> <a href="normform.html#K1" target="_self">\/</a> <span class="p2">(<span class="default"><font color="Maroon">a</font> <a href="normform.html#K2" target="_self">/\</a> <font color="Maroon">c</font></span>)</span></span>)</span> <a href="domain_1.html#K2">`1</a> 
<b>by </b><i/>
;<br/><b>thus </b><span class="p1">(<span class="default"><font color="Maroon">a</font> <a href="normform.html#K2" target="_self">/\</a> <span class="p2">(<span class="default"><font color="Maroon">b</font> <a href="normform.html#K1" target="_self">\/</a> <font color="Maroon">c</font></span>)</span></span>)</span> <a href="domain_1.html#K3">`2</a>  = 
<span class="p1">(<span class="default"><font color="Maroon">a</font> <a href="domain_1.html#K3">`2</a> </span>)</span> <a href="finsub_1.html#K3">/\</a> <span class="p1">(<span class="default"><span class="p2">(<span class="default"><font color="Maroon">b</font> <a href="normform.html#K1" target="_self">\/</a> <font color="Maroon">c</font></span>)</span> <a href="domain_1.html#K3">`2</a> </span>)</span>
<b>by </b><i/>
<br/>.= 
<span class="p1">(<span class="default"><font color="Maroon">a</font> <a href="domain_1.html#K3">`2</a> </span>)</span> <a href="finsub_1.html#K3">/\</a> <span class="p1">(<span class="default"><span class="p2">(<span class="default"><font color="Maroon">b</font> <a href="domain_1.html#K3">`2</a> </span>)</span> <a href="finsub_1.html#K1">\/</a> <span class="p2">(<span class="default"><font color="Maroon">c</font> <a href="domain_1.html#K3">`2</a> </span>)</span></span>)</span>
<b>by </b><i/>
<br/>.= 
<span class="p1">(<span class="default"><span class="p2">(<span class="default"><font color="Maroon">a</font> <a href="domain_1.html#K3">`2</a> </span>)</span> <a href="finsub_1.html#K3">/\</a> <span class="p2">(<span class="default"><font color="Maroon">b</font> <a href="domain_1.html#K3">`2</a> </span>)</span></span>)</span> <a href="finsub_1.html#K1">\/</a> <span class="p1">(<span class="default"><span class="p2">(<span class="default"><font color="Maroon">a</font> <a href="domain_1.html#K3">`2</a> </span>)</span> <a href="finsub_1.html#K3">/\</a> <span class="p2">(<span class="default"><font color="Maroon">c</font> <a href="domain_1.html#K3">`2</a> </span>)</span></span>)</span>
<b>by </b><i><a class="ref" href="xboole_1.html#T23">XBOOLE_1:23</a></i>
<br/>.= 
<span class="p1">(<span class="default"><span class="p2">(<span class="default"><font color="Maroon">a</font> <a href="domain_1.html#K3">`2</a> </span>)</span> <a href="finsub_1.html#K3">/\</a> <span class="p2">(<span class="default"><font color="Maroon">b</font> <a href="domain_1.html#K3">`2</a> </span>)</span></span>)</span> <a href="finsub_1.html#K1">\/</a> <span class="p1">(<span class="default"><span class="p2">(<span class="default"><font color="Maroon">a</font> <a href="normform.html#K2" target="_self">/\</a> <font color="Maroon">c</font></span>)</span> <a href="domain_1.html#K3">`2</a> </span>)</span>
<b>by </b><i/>
<br/>.= 
<span class="p1">(<span class="default"><span class="p2">(<span class="default"><font color="Maroon">a</font> <a href="normform.html#K2" target="_self">/\</a> <font color="Maroon">b</font></span>)</span> <a href="domain_1.html#K3">`2</a> </span>)</span> <a href="finsub_1.html#K1">\/</a> <span class="p1">(<span class="default"><span class="p2">(<span class="default"><font color="Maroon">a</font> <a href="normform.html#K2" target="_self">/\</a> <font color="Maroon">c</font></span>)</span> <a href="domain_1.html#K3">`2</a> </span>)</span>
<b>by </b><i/>
<br/>.= 
<span class="p1">(<span class="default"><span class="p2">(<span class="default"><font color="Maroon">a</font> <a href="normform.html#K2" target="_self">/\</a> <font color="Maroon">b</font></span>)</span> <a href="normform.html#K1" target="_self">\/</a> <span class="p2">(<span class="default"><font color="Maroon">a</font> <a href="normform.html#K2" target="_self">/\</a> <font color="Maroon">c</font></span>)</span></span>)</span> <a href="domain_1.html#K3">`2</a> 
<b>by </b><i/>
;<br/></div><b>end;</b></div>
<b>hence </b><a NAME="E2:6"/>
<font color="Maroon">a</font> <a href="normform.html#K2" target="_self">/\</a> <span class="p1">(<span class="default"><font color="Maroon">b</font> <a href="normform.html#K1" target="_self">\/</a> <font color="Maroon">c</font></span>)</span> <a href="hidden.html#R1">=</a> <span class="p1">(<span class="default"><font color="Maroon">a</font> <a href="normform.html#K2" target="_self">/\</a> <font color="Maroon">b</font></span>)</span> <a href="normform.html#K1" target="_self">\/</a> <span class="p1">(<span class="default"><font color="Maroon">a</font> <a href="normform.html#K2" target="_self">/\</a> <font color="Maroon">c</font></span>)</span>
 <b>by </b><i><a class="ref" href="domain_1.html#T12">DOMAIN_1:12</a></i>;<br/>


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