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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">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>assume </b><b>that </b><br/><a NAME="E1:124"/><i><font color="Green">E26</font></i>: 
<span class="p1"><a href="zfmisc_1.html#K2" target="_self">[:</a><span class="default"><font color="Maroon">X1</font>,<font color="Maroon">X2</font></span><a href="zfmisc_1.html#K2" target="_self">:]</a></span> <a href="tarski.html#R1">c=</a> <span class="p1"><a href="zfmisc_1.html#K2" target="_self">[:</a><span class="default"><font color="Maroon">Y1</font>,<font color="Maroon">Y2</font></span><a href="zfmisc_1.html#K2" target="_self">:]</a></span>
 <b>and </b><br/><a NAME="E2:124"/><i><font color="Green">E31</font></i>: 
<span class="p1"><a href="zfmisc_1.html#K2" target="_self">[:</a><span class="default"><font color="Maroon">X1</font>,<font color="Maroon">X2</font></span><a href="zfmisc_1.html#K2" target="_self">:]</a></span> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a>  <a href="xboole_0.html#K1">{}</a> 
 ;<br/>

<a NAME="E3:124"/><i><font color="Green">E32</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>  )
 
<b>by </b><i>, <a class="txt" href="zfmisc_1.html#E28"><i><font color="Green">Lemma45</font></i></a></i>;<br/>
<span class="p1"><a href="zfmisc_1.html#K2" target="_self">[:</a><span class="default"><font color="Maroon">X1</font>,<font color="Maroon">X2</font></span><a href="zfmisc_1.html#K2" target="_self">:]</a></span> = 
<span class="p1"><a href="zfmisc_1.html#K2" target="_self">[:</a><span class="default"><font color="Maroon">X1</font>,<font color="Maroon">X2</font></span><a href="zfmisc_1.html#K2" target="_self">:]</a></span> <a href="xboole_0.html#K3">/\</a> <span class="p1"><a href="zfmisc_1.html#K2" target="_self">[:</a><span class="default"><font color="Maroon">Y1</font>,<font color="Maroon">Y2</font></span><a href="zfmisc_1.html#K2" target="_self">:]</a></span>
<b>by </b><i>, <a class="ref" href="xboole_1.html#T28">XBOOLE_1:28</a></i>
<br/>.= 
<span class="p1"><a href="zfmisc_1.html#K2" target="_self">[:</a><span class="default"><span class="p2">(<span class="default"><font color="Maroon">X1</font> <a href="xboole_0.html#K3">/\</a> <font color="Maroon">Y1</font></span>)</span>,<span class="p2">(<span class="default"><font color="Maroon">X2</font> <a href="xboole_0.html#K3">/\</a> <font color="Maroon">Y2</font></span>)</span></span><a href="zfmisc_1.html#K2" target="_self">:]</a></span>
<b>by </b><i><a class="txt" href="zfmisc_1.html#E34"><i><font color="Green">Lemma49</font></i></a></i>
;<br/>
<a NAME="E5:124"/><b>then </b>
( <font color="Maroon">X1</font> <a href="hidden.html#R1">=</a> <font color="Maroon">X1</font> <a href="xboole_0.html#K3">/\</a> <font color="Maroon">Y1</font> &amp; <font color="Maroon">X2</font> <a href="hidden.html#R1">=</a> <font color="Maroon">X2</font> <a href="xboole_0.html#K3">/\</a> <font color="Maroon">Y2</font> )
 
<b>by </b><i>, <a class="txt" href="zfmisc_1.html#E46"><i><font color="Green">Lemma54</font></i></a></i>;<br/>
<b>hence </b><a NAME="E6:124"/>
( <font color="Maroon">X1</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">Y1</font> &amp; <font color="Maroon">X2</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">Y2</font> )
 <b>by </b><i><a class="ref" href="xboole_1.html#T17">XBOOLE_1:17</a></i>;<br/>


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