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<b>thus </b><a NAME="E1:79_1_1"/>
( <font color="Maroon">X</font> <a href="hidden.html#R1">=</a> <font color="Maroon">Y</font> implies for <font color="Olive">c</font> being <a href="xcmplx_0.html#V1">complex</a>  <a href="ordinal1.html#NM1" target="_self">number</a>  holds <br/> ( <font color="Olive">c</font> <a href="hidden.html#R2">in</a> <font color="Maroon">X</font> iff <font color="Olive">c</font> <a href="hidden.html#R2">in</a> <font color="Maroon">Y</font> ) )
 ;<br/>

<b>assume </b><a NAME="E2:79_1_1"/>
for <font color="Olive">c</font> being <a href="xcmplx_0.html#V1">complex</a>  <a href="ordinal1.html#NM1" target="_self">number</a>  holds <br/> ( <font color="Olive">c</font> <a href="hidden.html#R2">in</a> <font color="Maroon">X</font> iff <font color="Olive">c</font> <a href="hidden.html#R2">in</a> <font color="Maroon">Y</font> )
 ;<br/>

<b>hence </b><a NAME="E3:79_1_1"/>
( <font color="Maroon">X</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">Y</font> &amp; <font color="Maroon">Y</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">X</font> )
 <b>by </b><i><a class="ref" href="membered.html#D5" target="_self">Def5</a></i>; <i><font color="Red">:: according to </font></i><a class="ref" href="xboole_0.html#D10">XBOOLE_0:def 10</a><br/>


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