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

<a NAME="E1:60"/><i><font color="Green">E19</font></i>: 
(  <a href="xboole_0.html#K1">{}</a>  <a href="ordinal1.html#R1">c=</a> <font color="Maroon">A</font> &amp; <a href="xboole_0.html#K1">{}</a>  <a href="ordinal2.html#K10">+^</a> <font color="Maroon">A</font> <a href="hidden.html#R1">=</a> <font color="Maroon">A</font> )
 
<b>by </b><i><a class="ref" href="ordinal2.html#T47">ORDINAL2:47</a>, <a class="ref" href="xboole_1.html#T2">XBOOLE_1:2</a></i>;<br/>
<b>hence </b><a NAME="E2:60"/>
<font color="Maroon">A</font> <a href="ordinal3.html#K5" target="_self">-^</a> <a href="xboole_0.html#K1">{}</a>  <a href="hidden.html#R1">=</a> <font color="Maroon">A</font>
 <b>by </b><i/>;<br/>

<a NAME="E3:60"/>
(  not <font color="Maroon">A</font> <a href="ordinal1.html#R1">c=</a>  <a href="xboole_0.html#K1">{}</a>  or <font color="Maroon">A</font> <a href="ordinal1.html#R1">c=</a>  <a href="xboole_0.html#K1">{}</a>  )
 
;<br/>
<a NAME="E4:60"/><b>then </b>
( <a href="xboole_0.html#K1">{}</a>  <a href="ordinal3.html#K5" target="_self">-^</a> <font color="Maroon">A</font> <a href="hidden.html#R1">=</a>  <a href="xboole_0.html#K1">{}</a>  or <font color="Maroon">A</font> <a href="hidden.html#R1">=</a>  <a href="xboole_0.html#K1">{}</a>  )
 
<b>by </b><i>, <a class="ref" href="xboole_1.html#T3">XBOOLE_1:3</a></i>;<br/>
<b>hence </b><a NAME="E5:60"/>
<a href="xboole_0.html#K1">{}</a>  <a href="ordinal3.html#K5" target="_self">-^</a> <font color="Maroon">A</font> <a href="hidden.html#R1">=</a>  <a href="xboole_0.html#K1">{}</a> 
 <b>by </b><i>, </i>;<br/>


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