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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>set </b><font color="Maroon">h</font> = <font color="Maroon">x1</font>,<font color="Maroon">x2</font> <a href="funct_4.html#K4" target="_self">--&gt;</a> <font color="Maroon">y1</font>,<font color="Maroon">y2</font>;<br/>
<b>assume </b><a NAME="E1:69"/><i><font color="Green">E34</font></i>: 
<font color="Maroon">x1</font> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a> <font color="Maroon">x2</font>
 ;<br/>

<b>thus </b><a NAME="E2:69"/>
 <a href="relat_1.html#K2">rng</a> <span class="p1">(<span class="default"><font color="Maroon">x1</font>,<font color="Maroon">x2</font> <a href="funct_4.html#K4" target="_self">--&gt;</a> <font color="Maroon">y1</font>,<font color="Maroon">y2</font></span>)</span> <a href="tarski.html#R1">c=</a> <span class="p1"><a href="tarski.html#K2">{</a><span class="default"><font color="Maroon">y1</font>,<font color="Maroon">y2</font></span><a href="tarski.html#K2">}</a></span>
 <b>by </b><i/>; <i><font color="Red">:: according to </font></i><a class="ref" href="xboole_0.html#D10">XBOOLE_0:def 10</a><br/>

<b>let </b><font color="Maroon">y</font> be    <a href="hidden.html#M1">set</a> ; <i><font color="Red">:: according to </font></i><a class="ref" href="tarski.html#D3">TARSKI:def 3</a><br/>

<b>assume </b><a NAME="E3:69"/>
<font color="Maroon">y</font> <a href="hidden.html#R2">in</a> <span class="p1"><a href="tarski.html#K2">{</a><span class="default"><font color="Maroon">y1</font>,<font color="Maroon">y2</font></span><a href="tarski.html#K2">}</a></span>
 ;<br/>

<a NAME="E4:69"/><b>then </b>
( ( <font color="Maroon">y</font> <a href="hidden.html#R1">=</a> <font color="Maroon">y1</font> or <font color="Maroon">y</font> <a href="hidden.html#R1">=</a> <font color="Maroon">y2</font> ) &amp;  <a href="relat_1.html#K1">dom</a> <span class="p1">(<span class="default"><font color="Maroon">x1</font>,<font color="Maroon">x2</font> <a href="funct_4.html#K4" target="_self">--&gt;</a> <font color="Maroon">y1</font>,<font color="Maroon">y2</font></span>)</span> <a href="hidden.html#R1">=</a> <span class="p1"><a href="tarski.html#K2">{</a><span class="default"><font color="Maroon">x1</font>,<font color="Maroon">x2</font></span><a href="tarski.html#K2">}</a></span> )
 
<b>by </b><i>, <a class="ref" href="tarski.html#D2">TARSKI:def 2</a></i>;<br/>
<a NAME="E5:69"/><b>then </b>
( ( <span class="p1">(<span class="default"><font color="Maroon">x1</font>,<font color="Maroon">x2</font> <a href="funct_4.html#K4" target="_self">--&gt;</a> <font color="Maroon">y1</font>,<font color="Maroon">y2</font></span>)</span> <a href="funct_1.html#K1">.</a> <font color="Maroon">x1</font> <a href="hidden.html#R1">=</a> <font color="Maroon">y</font> or <span class="p1">(<span class="default"><font color="Maroon">x1</font>,<font color="Maroon">x2</font> <a href="funct_4.html#K4" target="_self">--&gt;</a> <font color="Maroon">y1</font>,<font color="Maroon">y2</font></span>)</span> <a href="funct_1.html#K1">.</a> <font color="Maroon">x2</font> <a href="hidden.html#R1">=</a> <font color="Maroon">y</font> ) &amp; <font color="Maroon">x1</font> <a href="hidden.html#R2">in</a>  <a href="relat_1.html#K1">dom</a> <span class="p1">(<span class="default"><font color="Maroon">x1</font>,<font color="Maroon">x2</font> <a href="funct_4.html#K4" target="_self">--&gt;</a> <font color="Maroon">y1</font>,<font color="Maroon">y2</font></span>)</span> &amp; <font color="Maroon">x2</font> <a href="hidden.html#R2">in</a>  <a href="relat_1.html#K1">dom</a> <span class="p1">(<span class="default"><font color="Maroon">x1</font>,<font color="Maroon">x2</font> <a href="funct_4.html#K4" target="_self">--&gt;</a> <font color="Maroon">y1</font>,<font color="Maroon">y2</font></span>)</span> )
 
<b>by </b><i>, , <a class="ref" href="tarski.html#D2">TARSKI:def 2</a></i>;<br/>
<b>hence </b><a NAME="E6:69"/>
<font color="Maroon">y</font> <a href="hidden.html#R2">in</a>  <a href="relat_1.html#K2">rng</a> <span class="p1">(<span class="default"><font color="Maroon">x1</font>,<font color="Maroon">x2</font> <a href="funct_4.html#K4" target="_self">--&gt;</a> <font color="Maroon">y1</font>,<font color="Maroon">y2</font></span>)</span>
 <b>by </b><i><a class="ref" href="funct_1.html#D5">FUNCT_1:def 5</a></i>;<br/>


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