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

<b>assume </b><a NAME="E1:17"/><i><font color="Green">E19</font></i>: 
( <font color="Maroon">A</font> <a href="ordinal1.html#R1">c=</a> 1 &amp; <font color="Maroon">A</font> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a>  <a href="xboole_0.html#K1">{}</a>  &amp; <font color="Maroon">A</font> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a> 1 )
 ;<br/>

<a NAME="E2:17"/><b>then </b>
<font color="Maroon">A</font> <a href="xboole_0.html#R2">c&lt;</a> 1
 
<b>by </b><i><a class="ref" href="xboole_0.html#D8">XBOOLE_0:def 8</a></i>;<br/>
<a NAME="E3:17"/><b>then </b>
<font color="Maroon">A</font> <a href="hidden.html#R2">in</a> 1
 
<b>by </b><i><a class="ref" href="ordinal1.html#T21">ORDINAL1:21</a></i>;<br/>
<b>hence </b><a NAME="E4:17"/>
contradiction
 <b>by </b><i>, </i>;<br/>


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