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<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="E1:23"/><i><font color="Green">E19</font></i>: 
( <font color="Maroon">B</font> <a href="ordinal2.html#K10">+^</a> <font color="Maroon">C</font> <a href="hidden.html#R2">in</a> <font color="Maroon">B</font> <a href="ordinal2.html#K10">+^</a> <font color="Maroon">D</font> &amp; not <font color="Maroon">C</font> <a href="hidden.html#R2">in</a> <font color="Maroon">D</font> )
 ;<br/>

<a NAME="E2:23"/><b>then </b>
<font color="Maroon">D</font> <a href="ordinal1.html#R1">c=</a> <font color="Maroon">C</font>
 
<b>by </b><i><a class="ref" href="ordinal1.html#T26">ORDINAL1:26</a></i>;<br/>
<a NAME="E3:23"/><b>then </b>
<font color="Maroon">B</font> <a href="ordinal2.html#K10">+^</a> <font color="Maroon">D</font> <a href="ordinal1.html#R1">c=</a> <font color="Maroon">B</font> <a href="ordinal2.html#K10">+^</a> <font color="Maroon">C</font>
 
<b>by </b><i><a class="ref" href="ordinal2.html#T50">ORDINAL2:50</a></i>;<br/>
<b>hence </b><a NAME="E4:23"/>
contradiction
 <b>by </b><i>, <a class="ref" href="ordinal1.html#T7">ORDINAL1:7</a></i>;<br/>


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