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<b>let </b><font color="Maroon">X</font> be    <a href="hidden.html#M1">set</a> ;<br/><b>let </b><font color="Maroon">Y</font> be    <a href="hidden.html#M1">set</a> ;<br/>



<b>assume </b><a NAME="E1:27"/>
<font color="Maroon">X</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">Y</font>
 ;<br/>

<a NAME="E2:27"/><b>then </b>
(  <a href="ordinal1.html#K3">On</a> <font color="Maroon">X</font> <a href="tarski.html#R1">c=</a>  <a href="ordinal1.html#K3">On</a> <font color="Maroon">Y</font> &amp;  <a href="ordinal1.html#K3">On</a> <font color="Maroon">Y</font> <a href="tarski.html#R1">c=</a>  <a href="ordinal2.html#K3" target="_self">sup</a> <font color="Maroon">Y</font> )
 
<b>by </b><i>, </i>;<br/>
<a NAME="E3:27"/><b>then </b>
(  <a href="ordinal1.html#K3">On</a> <font color="Maroon">X</font> <a href="tarski.html#R1">c=</a>  <a href="ordinal2.html#K3" target="_self">sup</a> <font color="Maroon">Y</font> &amp; ( for <font color="Olive">A</font> being  <a href="ordinal1.html#NM2">Ordinal</a>  st  <a href="ordinal1.html#K3">On</a> <font color="Maroon">X</font> <a href="tarski.html#R1">c=</a> <font color="Olive">A</font> holds <br/> <a href="ordinal2.html#K3" target="_self">sup</a> <font color="Maroon">X</font> <a href="ordinal1.html#R1">c=</a> <font color="Olive">A</font> ) )
 
<b>by </b><i>, <a class="ref" href="xboole_1.html#T1">XBOOLE_1:1</a></i>;<br/>
<b>hence </b><a NAME="E4:27"/>
 <a href="ordinal2.html#K3" target="_self">sup</a> <font color="Maroon">X</font> <a href="ordinal1.html#R1">c=</a>  <a href="ordinal2.html#K3" target="_self">sup</a> <font color="Maroon">Y</font>
 ;<br/>


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