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<b>let </b><font color="Maroon">X'</font> be    <a href="hidden.html#M1">set</a> ;<br/><b>let </b><font color="Maroon">Y'</font> be    <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">Y</font> be    <a href="hidden.html#M1">set</a> ;<br/>







<b>assume </b><a NAME="E1:71"/>
<font color="Maroon">X'</font> <a href="xboole_0.html#K2">\/</a> <font color="Maroon">Y'</font> <a href="hidden.html#R1">=</a> <font color="Maroon">X</font> <a href="xboole_0.html#K2">\/</a> <font color="Maroon">Y</font>
 ;<br/>

<a NAME="E2:71"/><b>then </b><i><font color="Green">E13</font></i>: 
( <font color="Maroon">X</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">X'</font> <a href="xboole_0.html#K2">\/</a> <font color="Maroon">Y'</font> &amp; <font color="Maroon">Y</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">X'</font> <a href="xboole_0.html#K2">\/</a> <font color="Maroon">Y'</font> &amp; <font color="Maroon">X'</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">X</font> <a href="xboole_0.html#K2">\/</a> <font color="Maroon">Y</font> &amp; <font color="Maroon">Y'</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">X</font> <a href="xboole_0.html#K2">\/</a> <font color="Maroon">Y</font> )
 
<b>by </b><i/>;<br/>
<b>assume </b><a NAME="E3:71"/>
( <font color="Maroon">X</font> <a href="xboole_0.html#R1">misses</a> <font color="Maroon">X'</font> &amp; <font color="Maroon">Y</font> <a href="xboole_0.html#R1">misses</a> <font color="Maroon">Y'</font> )
 ;<br/>

<a NAME="E4:71"/><b>then </b><i><font color="Green">E14</font></i>: 
( <font color="Maroon">X</font> <a href="xboole_0.html#K3">/\</a> <font color="Maroon">X'</font> <a href="hidden.html#R1">=</a>  <a href="xboole_0.html#K1">{}</a>  &amp; <font color="Maroon">Y</font> <a href="xboole_0.html#K3">/\</a> <font color="Maroon">Y'</font> <a href="hidden.html#R1">=</a>  <a href="xboole_0.html#K1">{}</a>  )
 
<b>by </b><i><a class="ref" href="xboole_0.html#D7">XBOOLE_0:def 7</a></i>;<br/>
<b>thus </b><font color="Maroon">X</font> = 
<font color="Maroon">X</font> <a href="xboole_0.html#K3">/\</a> <span class="p1">(<span class="default"><font color="Maroon">X'</font> <a href="xboole_0.html#K2">\/</a> <font color="Maroon">Y'</font></span>)</span>
<b>by </b><i><a class="ref" href="xboole_1.html#T36" target="_self">Th36</a>, <a class="ref" href="xboole_1.html#T3" target="_self">Th3</a></i>
<br/>.= 
<span class="p1">(<span class="default"><font color="Maroon">X</font> <a href="xboole_0.html#K3">/\</a> <font color="Maroon">X'</font></span>)</span> <a href="xboole_0.html#K2">\/</a> <span class="p1">(<span class="default"><font color="Maroon">X</font> <a href="xboole_0.html#K3">/\</a> <font color="Maroon">Y'</font></span>)</span>
<b>by </b><i><a class="txt" href="xboole_1.html#E2:71"><i><font color="Green">E13</font></i></a></i>
<br/>.= 
<span class="p1">(<span class="default"><font color="Maroon">X</font> <a href="xboole_0.html#K2">\/</a> <font color="Maroon">Y</font></span>)</span> <a href="xboole_0.html#K3">/\</a> <font color="Maroon">Y'</font>
<b>by </b><i><a class="ref" href="xboole_1.html#T39" target="_self">Th39</a>, <a class="txt" href="xboole_1.html#E2:71"><i><font color="Green">E13</font></i></a></i>
<br/>.= 
<font color="Maroon">Y'</font>
<b>by </b><i><a class="ref" href="xboole_1.html#T36" target="_self">Th36</a>, <a class="ref" href="xboole_1.html#T3" target="_self">Th3</a></i>
;<br/>


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