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<b>let </b><font color="Maroon">GX</font> be  non <a href="struct_0.html#V3">empty</a> <a href="pre_topc.html#NM1">TopSpace</a>;<br/><b>let </b><font color="Maroon">B1</font> be   <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">GX</font>, <font color="Maroon">B2</font> be   <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">GX</font>, <font color="Maroon">V</font> be   <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">GX</font>;<br/>



<a NAME="E1:4"/>
(  <a href="connsp_3.html#K4">Down</a> <span class="p1">(<span class="default"><font color="Maroon">B1</font> <a href="subset_1.html#K4">\/</a> <font color="Maroon">B2</font></span>)</span>,<font color="Maroon">V</font> <a href="hidden.html#R1">=</a> <span class="p1">(<span class="default"><font color="Maroon">B1</font> <a href="subset_1.html#K4">\/</a> <font color="Maroon">B2</font></span>)</span> <a href="subset_1.html#K9">/\</a> <font color="Maroon">V</font> &amp;  <a href="connsp_3.html#K4">Down</a> <font color="Maroon">B1</font>,<font color="Maroon">V</font> <a href="hidden.html#R1">=</a> <font color="Maroon">B1</font> <a href="subset_1.html#K9">/\</a> <font color="Maroon">V</font> &amp;  <a href="connsp_3.html#K4">Down</a> <font color="Maroon">B2</font>,<font color="Maroon">V</font> <a href="hidden.html#R1">=</a> <font color="Maroon">B2</font> <a href="subset_1.html#K9">/\</a> <font color="Maroon">V</font> )
 
<b>by </b><i><a class="ref" href="connsp_3.html#D5">CONNSP_3:def 5</a></i>;<br/>
<b>hence </b><a NAME="E2:4"/>
 <a href="connsp_3.html#K4">Down</a> <span class="p1">(<span class="default"><font color="Maroon">B1</font> <a href="subset_1.html#K4">\/</a> <font color="Maroon">B2</font></span>)</span>,<font color="Maroon">V</font> <a href="hidden.html#R1">=</a> <span class="p1">(<span class="default"><a href="connsp_3.html#K4">Down</a> <font color="Maroon">B1</font>,<font color="Maroon">V</font></span>)</span> <a href="subset_1.html#K4">\/</a> <span class="p1">(<span class="default"><a href="connsp_3.html#K4">Down</a> <font color="Maroon">B2</font>,<font color="Maroon">V</font></span>)</span>
 <b>by </b><i><a class="ref" href="xboole_1.html#T23">XBOOLE_1:23</a></i>;<br/>


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