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<b>let </b><font color="Maroon">FMT</font> be  non <a href="struct_0.html#V3">empty</a>  <a href="fintopo2.html#L1" target="_self">FMT_Space_Str</a> ;<br/><b>let </b><font color="Maroon">A</font> be   <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">FMT</font>;<br/>



<b>assume </b><a NAME="E1:57"/>
<font color="Maroon">A</font> <a href="subset_1.html#K3">`</a>  is <a href="fintopo2.html#V4" target="_self">Fo_closed</a>
 ;<br/>

<a NAME="E2:57"/><b>then </b><i><font color="Green">E19</font></i>: 
<font color="Maroon">A</font> <a href="subset_1.html#K3">`</a>  <a href="hidden.html#R1">=</a> <span class="p1">(<span class="default"><font color="Maroon">A</font> <a href="subset_1.html#K3">`</a> </span>)</span> <a href="fintopo2.html#K9" target="_self">^Fob</a> 
 
<b>by </b><i/>;<br/>
<span class="p1">(<span class="default"><font color="Maroon">A</font> <a href="subset_1.html#K3">`</a> </span>)</span> <a href="fintopo2.html#K9" target="_self">^Fob</a>  = 
<span class="p1">(<span class="default"><span class="p2">(<span class="default"><span class="p3">(<span class="default"><font color="Maroon">A</font> <a href="subset_1.html#K3">`</a> </span>)</span> <a href="subset_1.html#K3">`</a> </span>)</span> <a href="fintopo2.html#K10" target="_self">^Foi</a> </span>)</span> <a href="subset_1.html#K3">`</a> 
<b>by </b><i/>
<br/>.= 
<span class="p1">(<span class="default"><font color="Maroon">A</font> <a href="fintopo2.html#K10" target="_self">^Foi</a> </span>)</span> <a href="subset_1.html#K3">`</a> 

;<br/>
<b>then </b><font color="Maroon">A</font> = 
<span class="p1">(<span class="default"><span class="p2">(<span class="default"><font color="Maroon">A</font> <a href="fintopo2.html#K10" target="_self">^Foi</a> </span>)</span> <a href="subset_1.html#K3">`</a> </span>)</span> <a href="subset_1.html#K3">`</a> 
<b>by </b><i/>
<br/>.= 
<font color="Maroon">A</font> <a href="fintopo2.html#K10" target="_self">^Foi</a> 

;<br/>
<b>hence </b><a NAME="E5:57"/>
<font color="Maroon">A</font> is <a href="fintopo2.html#V3" target="_self">Fo_open</a>
 <b>by </b><i/>;<br/>


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