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<b>take </b>
 <a href="xboole_0.html#K1">{}</a> 
;<br/>

<b>let </b><font color="Maroon">x</font> be    <a href="hidden.html#M1">set</a> , <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="facirc_1.html#D1" target="_self">FACIRC_1:def 1</a><br/>

<b>thus </b><a NAME="E1:4_2_1"/>
not  <a href="xboole_0.html#K1">{}</a>  <a href="hidden.html#R1">=</a> <span class="p1"><a href="tarski.html#K4">[</a><span class="default"><font color="Maroon">x</font>,<font color="Maroon">y</font></span><a href="tarski.html#K4">]</a></span>
 ;<br/>


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