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<b>let </b><font color="Maroon">c<sub>1</sub></font> be  non <a href="xboole_0.html#V1">empty</a> <a href="compts_1.html#V6">compact</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/>

<b>assume </b><a NAME="E1:28"/>
 <a href="pscomp_1.html#K19">SW-corner</a> <font color="Maroon">c<sub>1</sub></font> <a href="hidden.html#R1">=</a>  <a href="pscomp_1.html#K22">SE-corner</a> <font color="Maroon">c<sub>1</sub></font>
 ;<br/>

<b>then </b><span class="p1"><a href="euclid.html#K23">|[</a><span class="default"><span class="p2">(<span class="default"><a href="pscomp_1.html#K15">W-bound</a> <font color="Maroon">c<sub>1</sub></font></span>)</span>,<span class="p2">(<span class="default"><a href="pscomp_1.html#K18">S-bound</a> <font color="Maroon">c<sub>1</sub></font></span>)</span></span><a href="euclid.html#K23">]|</a></span> = 
 <a href="pscomp_1.html#K22">SE-corner</a> <font color="Maroon">c<sub>1</sub></font>

<br/>.= 
<span class="p1"><a href="euclid.html#K23">|[</a><span class="default"><span class="p2">(<span class="default"><a href="pscomp_1.html#K17">E-bound</a> <font color="Maroon">c<sub>1</sub></font></span>)</span>,<span class="p2">(<span class="default"><a href="pscomp_1.html#K18">S-bound</a> <font color="Maroon">c<sub>1</sub></font></span>)</span></span><a href="euclid.html#K23">]|</a></span>

;<br/>
<a NAME="E3:28"/><b>then </b>
 <a href="pscomp_1.html#K15">W-bound</a> <font color="Maroon">c<sub>1</sub></font> <a href="hidden.html#R1">=</a>  <a href="pscomp_1.html#K17">E-bound</a> <font color="Maroon">c<sub>1</sub></font>
 
<b>by </b><i><a class="ref" href="sppol_2.html#T1">SPPOL_2:1</a></i>;<br/>
<b>hence </b><a NAME="E4:28"/>
<font color="Maroon">c<sub>1</sub></font> is <a href="sppol_1.html#V2">vertical</a>
 <b>by </b><i><a class="ref" href="sprect_1.html#T17" target="_self">Th17</a></i>;<br/>


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