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<b>consider </b><font color="Maroon">x</font> being    <a href="hidden.html#M1">set</a> <b> such that </b><br/><a NAME="E2:40_1_1"/><i><font color="Green">E24</font></i>: 
<font color="Maroon">x</font> <a href="hidden.html#R2">in</a> <font color="Maroon">X</font>
 <b>by </b><i><a class="ref" href="xboole_0.html#D1">XBOOLE_0:def 1</a></i>;<br/>
<a NAME="E3:40_1_1"/>
<span class="p1"><a href="tarski.html#K2">{</a><span class="default"><font color="Maroon">t</font>,<font color="Maroon">x</font></span><a href="tarski.html#K2">}</a></span> <a href="hidden.html#R2">in</a>  <a href="pencil_4.html#K9" target="_self">PairSet</a> <font color="Maroon">t</font>,<font color="Maroon">X</font>
 
<b>by </b><i>, </i>;<br/>
<b>hence </b><a NAME="E4:40_1_1"/>
not  <a href="pencil_4.html#K9" target="_self">PairSet</a> <font color="Maroon">t</font>,<font color="Maroon">X</font> is <a href="xboole_0.html#V1">empty</a>
 ;<br/>


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