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<b>let </b><font color="Maroon">U1</font> be   <a href="classes2.html#NM1">Universe</a>;<br/><b>let </b><font color="Maroon">U2</font> be   <a href="classes2.html#NM1">Universe</a>;<br/>



<a NAME="E1:52"/>
( (  <a href="ordinal1.html#K3">On</a> <font color="Maroon">U1</font> <a href="ordinal1.html#R1">c=</a>  <a href="ordinal1.html#K3">On</a> <font color="Maroon">U2</font> or  <a href="ordinal1.html#K3">On</a> <font color="Maroon">U2</font> <a href="ordinal1.html#R1">c=</a>  <a href="ordinal1.html#K3">On</a> <font color="Maroon">U1</font> ) &amp; <font color="Maroon">U1</font> <a href="hidden.html#R1">=</a>  <a href="classes1.html#K4">Rank</a> <span class="p1">(<span class="default"><a href="ordinal1.html#K3">On</a> <font color="Maroon">U1</font></span>)</span> &amp; <font color="Maroon">U2</font> <a href="hidden.html#R1">=</a>  <a href="classes1.html#K4">Rank</a> <span class="p1">(<span class="default"><a href="ordinal1.html#K3">On</a> <font color="Maroon">U2</font></span>)</span> )
 
<b>by </b><i><a class="ref" href="classes2.html#T4" target="_self">Th4</a></i>;<br/>
<b>hence </b><a NAME="E2:52"/>
( <font color="Maroon">U1</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">U2</font> or <font color="Maroon">U2</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">U1</font> )
 <b>by </b><i><a class="ref" href="classes1.html#T43">CLASSES1:43</a></i>; <i><font color="Red">:: according to </font></i><a class="ref" href="xboole_0.html#D9">XBOOLE_0:def 9</a><br/>


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