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<b>let </b><font color="Maroon">T</font> be  non <a href="struct_0.html#V3">empty</a> <a href="tdlat_3.html#V1">discrete</a> <a href="pre_topc.html#NM1">TopSpace</a>;<br/><b>let </b><font color="Maroon">W</font> be   <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">T</font>, <font color="Maroon">V</font> be   <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">T</font>; <i><font color="Red">:: according to </font></i><a class="ref" href="compts_1.html#D6">COMPTS_1:def 6</a><br/>



<b>assume </b><a NAME="E1:15"/><i><font color="Green">E28</font></i>: 
( <font color="Maroon">W</font> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a>  <a href="xboole_0.html#K1">{}</a>  &amp; <font color="Maroon">V</font> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a>  <a href="xboole_0.html#K1">{}</a>  &amp; <font color="Maroon">W</font> is <a href="pre_topc.html#V4">closed</a> &amp; <font color="Maroon">V</font> is <a href="pre_topc.html#V4">closed</a> &amp; <font color="Maroon">W</font> <a href="subset_1.html#K9">/\</a> <font color="Maroon">V</font> <a href="hidden.html#R1">=</a>  <a href="xboole_0.html#K1">{}</a>  )
 ; <i><font color="Red">:: according to </font></i><a class="ref" href="xboole_0.html#D7">XBOOLE_0:def 7</a><br/>

<b>take </b><font color="Maroon">P</font> = <font color="Maroon">W</font>;<br/>

<b>take </b><font color="Maroon">Q</font> = <font color="Maroon">V</font>;<br/>

<b>thus </b><a NAME="E2:15"/>
( <font color="Maroon">P</font> is <a href="pre_topc.html#V3">open</a> &amp; <font color="Maroon">Q</font> is <a href="pre_topc.html#V3">open</a> )
 <b>by </b><i><a class="ref" href="tdlat_3.html#T17">TDLAT_3:17</a></i>;<br/>

<b>thus </b><a NAME="E3:15"/>
( <font color="Maroon">W</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">P</font> &amp; <font color="Maroon">V</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">Q</font> &amp; <font color="Maroon">P</font> <a href="subset_1.html#K9">/\</a> <font color="Maroon">Q</font> <a href="hidden.html#R1">=</a>  <a href="xboole_0.html#K1">{}</a>  )
 <b>by </b><i/>; <i><font color="Red">:: according to </font></i><a class="ref" href="xboole_0.html#D7">XBOOLE_0:def 7</a><br/>


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