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<b>let </b><font color="Maroon">A</font> be   <a href="struct_0.html#NM2">Subset</a> of <span class="p1">(<span class="default"><a href="euclid.html#K15">TOP-REAL</a> 2</span>)</span>;<br/>

<b>assume </b><a NAME="E1:38_1_1"/><i><font color="Green">E56</font></i>: 
<font color="Maroon">A</font> is <a href="xboole_0.html#V1">empty</a>
 ;<br/>

<b>assume </b><a NAME="E2:38_1_1"/>
not <font color="Maroon">A</font> is <a href="sppol_1.html#V1">horizontal</a>
 ;<br/>

<b>then reconsider </b><font color="Maroon">B</font> = <font color="Maroon">A</font> as  non <a href="sppol_1.html#V1">horizontal</a> <a href="struct_0.html#NM2">Subset</a> of <span class="p1">(<span class="default"><a href="euclid.html#K15">TOP-REAL</a> 2</span>)</span> ;<br/>
<a NAME="E4:38_1_1"/>
not <font color="Maroon">B</font> is <a href="xboole_0.html#V1">empty</a>
 
;<br/>
<b>hence </b><a NAME="E5:38_1_1"/>
contradiction
 <b>by </b><i/>;<br/>


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