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<b>let </b><font color="Maroon" title="c1">O1</font>, <font color="Maroon" title="c2">O2</font> be   <a href="ordinal1.html#NM2" title="ORDINAL1:NM.2">Ordinal</a>;<br/>



<b>assume </b><a NAME="E1:41"/>
( not <font color="Maroon" title="c1">O1</font> <a href="xboole_0.html#R2" title="XBOOLE_0:pred.2">c&lt;</a> <font color="Maroon" title="c2">O2</font> &amp; not <font color="Maroon" title="c1">O1</font> <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a> <font color="Maroon" title="c2">O2</font> &amp; not <font color="Maroon" title="c2">O2</font> <a href="xboole_0.html#R2" title="XBOOLE_0:pred.2">c&lt;</a> <font color="Maroon" title="c1">O1</font> )
 ;<br/>

<a NAME="E2:41"/><b>then </b>
( not <font color="Maroon" title="c1">O1</font> <a href="ordinal1.html#R1" title="ORDINAL1:pred.1">c=</a> <font color="Maroon" title="c2">O2</font> &amp; not <font color="Maroon" title="c2">O2</font> <a href="ordinal1.html#R1" title="ORDINAL1:pred.1">c=</a> <font color="Maroon" title="c1">O1</font> )
 
<b>by </b><i><a class="ref" href="xboole_0.html#D8" title="XBOOLE_0:def.8">XBOOLE_0:def 8</a></i>;<br/>
<b>hence </b><a NAME="E3:41"/>
contradiction
 ;<br/>


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