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<b>let </b><font color="Maroon">Y</font> be  non <a href="struct_0.html#V3">empty</a> <a href="tdlat_3.html#V4" target="_self">extremally_disconnected</a> <a href="pre_topc.html#NM1">TopSpace</a>;<br/>

<a NAME="E1:68"/><i><font color="Green">E21</font></i>: 
 <a href="tdlat_1.html#K1">Domains_of</a> <font color="Maroon">Y</font> <a href="hidden.html#R1">=</a>  <a href="tdlat_1.html#K9">Open_Domains_of</a> <font color="Maroon">Y</font>
 
<b>by </b><i><a class="ref" href="tdlat_3.html#T15" target="_self">Th15</a></i>;<br/>
<b>hence </b> <a href="tdlat_1.html#NK3" target="_self">D-Union</a> <font color="Maroon">Y</font> = 
<span class="p1">(<span class="default"><a href="tdlat_1.html#NK3" target="_self">D-Union</a> <font color="Maroon">Y</font></span>)</span> <a href="realset1.html#K1">||</a> <span class="p1">(<span class="default"><a href="tdlat_1.html#K9">Open_Domains_of</a> <font color="Maroon">Y</font></span>)</span>
<b>by </b><i><a class="ref" href="funct_2.html#T40">FUNCT_2:40</a></i>
<br/>.= 
 <a href="tdlat_1.html#NK15" target="_self">OPD-Union</a> <font color="Maroon">Y</font>
<b>by </b><i><a class="ref" href="tdlat_1.html#T42">TDLAT_1:42</a></i>
;<br/><br/>

<b>thus </b> <a href="tdlat_1.html#NK5" target="_self">D-Meet</a> <font color="Maroon">Y</font> = 
<span class="p1">(<span class="default"><a href="tdlat_1.html#NK5" target="_self">D-Meet</a> <font color="Maroon">Y</font></span>)</span> <a href="realset1.html#K1">||</a> <span class="p1">(<span class="default"><a href="tdlat_1.html#K9">Open_Domains_of</a> <font color="Maroon">Y</font></span>)</span>
<b>by </b><i>, <a class="ref" href="funct_2.html#T40">FUNCT_2:40</a></i>
<br/>.= 
 <a href="tdlat_1.html#NK17" target="_self">OPD-Meet</a> <font color="Maroon">Y</font>
<b>by </b><i><a class="ref" href="tdlat_1.html#T43">TDLAT_1:43</a></i>
;<br/>


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