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<b>let </b><font color="Maroon">c<sub>1</sub></font> be   <a href="ordinal1.html#NM2">Ordinal</a>;<br/>

<a NAME="E1:58"/>
( <font color="Maroon">c<sub>1</sub></font> <a href="ordinal2.html#K10">+^</a> <a href="xboole_0.html#K1">{}</a>  <a href="hidden.html#R1">=</a> <font color="Maroon">c<sub>1</sub></font> &amp; <font color="Maroon">c<sub>1</sub></font> <a href="ordinal1.html#R1">c=</a> <font color="Maroon">c<sub>1</sub></font> )
 
<b>by </b><i><a class="ref" href="ordinal2.html#T44">ORDINAL2:44</a></i>;<br/>
<b>hence </b><a NAME="E2:58"/>
<font color="Maroon">c<sub>1</sub></font> <a href="ordinal3.html#K5" target="_self">-^</a> <font color="Maroon">c<sub>1</sub></font> <a href="hidden.html#R1">=</a>  <a href="xboole_0.html#K1">{}</a> 
 <b>by </b><i><a class="ref" href="ordinal3.html#D6" target="_self">Def6</a></i>;<br/>


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