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<b>assume </b><a NAME="E1:24_1_1"/>
<font color="Maroon">A</font> <a href="subset_1.html#K3">`</a>  is <a href="xboole_0.html#V1">empty</a>
 ;<br/>

<a NAME="E2:24_1_1"/><b>then </b>
<span class="p1">(<span class="default"><font color="Maroon">A</font> <a href="subset_1.html#K3">`</a> </span>)</span> <a href="subset_1.html#K3">`</a>  <a href="hidden.html#R1">=</a> <font color="Maroon">X</font>
 
;<br/>
<b>hence </b><a NAME="E3:24_1_1"/>
contradiction
 <b>by </b><i/>;<br/>


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