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<b>let </b><font color="Maroon">L</font> be   <a href="ordinal1.html#NM3">T-Sequence</a>;<br/><b>let </b><font color="Maroon">A</font> be   <a href="ordinal1.html#NM2">Ordinal</a>;<br/>



<a NAME="E1:15"/><i><font color="Green">E31</font></i>: 
 <a href="relat_1.html#K1">dom</a> <span class="p1">(<span class="default"><font color="Maroon">L</font> <a href="relat_1.html#K7">|</a> <span class="p2">(<span class="default"><a href="classes1.html#K4">Rank</a> <font color="Maroon">A</font></span>)</span></span>)</span> <a href="hidden.html#R1">=</a> <span class="p1">(<span class="default"><a href="relat_1.html#K1">dom</a> <font color="Maroon">L</font></span>)</span> <a href="xboole_0.html#K3">/\</a> <span class="p1">(<span class="default"><a href="classes1.html#K4">Rank</a> <font color="Maroon">A</font></span>)</span>
 
<b>by </b><i><a class="ref" href="relat_1.html#T90">RELAT_1:90</a></i>;<br/>
<div><a class="txt" onclick="hs2(this)" href="javascript:()" title="15_1"><b>now </b></a><div class="add"><b>let </b><font color="Maroon">X</font> be    <a href="hidden.html#M1">set</a> ;<br/><b>assume </b><a NAME="E1:15_1"/>
<font color="Maroon">X</font> <a href="hidden.html#R2">in</a>  <a href="relat_1.html#K1">dom</a> <span class="p1">(<span class="default"><font color="Maroon">L</font> <a href="relat_1.html#K7">|</a> <span class="p2">(<span class="default"><a href="classes1.html#K4">Rank</a> <font color="Maroon">A</font></span>)</span></span>)</span>
 ;<br/><a NAME="E2:15_1"/><b>then </b><i><font color="Green">E37</font></i>: 
( <font color="Maroon">X</font> <a href="hidden.html#R2">in</a>  <a href="relat_1.html#K1">dom</a> <font color="Maroon">L</font> &amp; <font color="Maroon">X</font> <a href="hidden.html#R2">in</a>  <a href="classes1.html#K4">Rank</a> <font color="Maroon">A</font> )
 <b>by </b><i>, <a class="ref" href="xboole_0.html#D3">XBOOLE_0:def 3</a></i>;<br/><b>hence </b><a NAME="E3:15_1"/>
<font color="Maroon">X</font> is   <a href="ordinal1.html#NM2">Ordinal</a>
 <b>by </b><i><a class="ref" href="ordinal1.html#T23">ORDINAL1:23</a></i>;<br/><a NAME="E4:15_1"/>
( <font color="Maroon">X</font> <a href="tarski.html#R1">c=</a>  <a href="relat_1.html#K1">dom</a> <font color="Maroon">L</font> &amp; <font color="Maroon">X</font> <a href="tarski.html#R1">c=</a>  <a href="classes1.html#K4">Rank</a> <font color="Maroon">A</font> )
 <b>by </b><i>, <a class="ref" href="ordinal1.html#D2">ORDINAL1:def 2</a></i>;<br/><b>hence </b><a NAME="E5:15_1"/>
<font color="Maroon">X</font> <a href="tarski.html#R1">c=</a>  <a href="relat_1.html#K1">dom</a> <span class="p1">(<span class="default"><font color="Maroon">L</font> <a href="relat_1.html#K7">|</a> <span class="p2">(<span class="default"><a href="classes1.html#K4">Rank</a> <font color="Maroon">A</font></span>)</span></span>)</span>
 <b>by </b><i>, <a class="ref" href="xboole_1.html#T19">XBOOLE_1:19</a></i>;<br/></div><b>end;</b></div>
<a NAME="E3:15"/><b>then </b>
 <a href="relat_1.html#K1">dom</a> <span class="p1">(<span class="default"><font color="Maroon">L</font> <a href="relat_1.html#K7">|</a> <span class="p2">(<span class="default"><a href="classes1.html#K4">Rank</a> <font color="Maroon">A</font></span>)</span></span>)</span> is   <a href="ordinal1.html#NM2">Ordinal</a>
 
<b>by </b><i><a class="ref" href="ordinal1.html#T31">ORDINAL1:31</a></i>;<br/>
<b>hence </b><a NAME="E4:15"/>
<font color="Maroon">L</font> <a href="relat_1.html#K7">|</a> <span class="p1">(<span class="default"><a href="classes1.html#K4">Rank</a> <font color="Maroon">A</font></span>)</span> is   <a href="ordinal1.html#NM3">T-Sequence</a>
 <b>by </b><i><a class="ref" href="ordinal1.html#T46">ORDINAL1:46</a></i>;<br/>


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