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<b>let </b><font color="Maroon" title="c1">SFX</font> be    <a href="hidden.html#M1" title="HIDDEN:mode.1">set</a> ;<br/><b>let </b><font color="Maroon" title="c2">X</font> be    <a href="hidden.html#M1" title="HIDDEN:mode.1">set</a> ; <i><font color="Red">:: according to </font></i><a class="ref" href="setfam_1.html#D2" target="_self" title="SETFAM_1:def.2">SETFAM_1:def 2</a><br/>



<b>assume </b><a NAME="E1:20"/><i><font color="Green" title="E8">A1</font></i>: 
<font color="Maroon" title="c2">X</font> <a href="hidden.html#R2" title="HIDDEN:pred.2">in</a> <font color="Maroon" title="c1">SFX</font>
 ;<br/>

<b>take </b>
<font color="Maroon" title="c2">X</font>
;<br/>

<a NAME="E2:20"/>
<font color="Maroon" title="c2">X</font> <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a> <font color="Maroon" title="c2">X</font> <a href="xboole_0.html#K2" title="XBOOLE_0:func.2">\/</a> <font color="Maroon" title="c2">X</font>
 
;<br/>
<b>hence </b><a NAME="E3:20"/>
( <font color="Maroon" title="c2">X</font> <a href="hidden.html#R2" title="HIDDEN:pred.2">in</a>  <a href="setfam_1.html#K2" title="SETFAM_1:func.2">UNION</a> <font color="Maroon" title="c1">SFX</font>,<font color="Maroon" title="c1">SFX</font> &amp; <font color="Maroon" title="c2">X</font> <a href="tarski.html#R1" title="TARSKI:pred.1">c=</a> <font color="Maroon" title="c2">X</font> )
 <b>by </b><i><a class="txt" href="setfam_1.html#E1:20"><i><font color="Green" title="E8">A1</font></i></a>, <a class="ref" href="setfam_1.html#D4" target="_self" title="SETFAM_1:def.4">Def4</a></i>;<br/>


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