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<b>let </b><font color="Maroon">A</font> be   <a href="ordinal1.html#NM2">Ordinal</a>;<br/><b>let </b><font color="Maroon">B</font> be   <a href="ordinal1.html#NM2">Ordinal</a>;<br/><b>let </b><font color="Maroon">C</font> be   <a href="ordinal1.html#NM2">Ordinal</a>;<br/><b>let </b><font color="Maroon">D</font> be   <a href="ordinal1.html#NM2">Ordinal</a>;<br/>







<b>assume </b><a NAME="E1:20"/><i><font color="Green">E19</font></i>: 
( <font color="Maroon">A</font> <a href="hidden.html#R2">in</a> <font color="Maroon">B</font> &amp; ( ( <font color="Maroon">C</font> <a href="ordinal1.html#R1">c=</a> <font color="Maroon">D</font> &amp; <font color="Maroon">D</font> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a>  <a href="xboole_0.html#K1">{}</a>  ) or <font color="Maroon">C</font> <a href="hidden.html#R2">in</a> <font color="Maroon">D</font> ) )
 ;<br/>

<a NAME="E2:20"/><b>then </b>
( <font color="Maroon">C</font> <a href="ordinal1.html#R1">c=</a> <font color="Maroon">D</font> &amp; <font color="Maroon">D</font> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a>  <a href="xboole_0.html#K1">{}</a>  )
 
<b>by </b><i><a class="ref" href="ordinal1.html#D2">ORDINAL1:def 2</a></i>;<br/>
<a NAME="E3:20"/><b>then </b>
( <font color="Maroon">A</font> <a href="ordinal2.html#K11">*^</a> <font color="Maroon">C</font> <a href="ordinal1.html#R1">c=</a> <font color="Maroon">A</font> <a href="ordinal2.html#K11">*^</a> <font color="Maroon">D</font> &amp; <font color="Maroon">A</font> <a href="ordinal2.html#K11">*^</a> <font color="Maroon">D</font> <a href="hidden.html#R2">in</a> <font color="Maroon">B</font> <a href="ordinal2.html#K11">*^</a> <font color="Maroon">D</font> )
 
<b>by </b><i>, <a class="ref" href="ordinal2.html#T57">ORDINAL2:57</a>, <a class="ref" href="ordinal2.html#T59">ORDINAL2:59</a></i>;<br/>
<b>hence </b><a NAME="E4:20"/>
<font color="Maroon">A</font> <a href="ordinal2.html#K11">*^</a> <font color="Maroon">C</font> <a href="hidden.html#R2">in</a> <font color="Maroon">B</font> <a href="ordinal2.html#K11">*^</a> <font color="Maroon">D</font>
 <b>by </b><i><a class="ref" href="ordinal1.html#T22">ORDINAL1:22</a></i>;<br/>


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