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<b>let </b><font color="Maroon">T</font> be    <a href="pre_topc.html#L1">TopStruct</a> ;<br/><b>let </b><font color="Maroon">A</font> be    <a href="pre_topc.html#M1">SubSpace</a> of <font color="Maroon">T</font>;<br/><b>let </b><font color="Maroon">F</font> be   <a href="struct_0.html#NM3">Subset-Family</a> of <font color="Maroon">A</font>;<br/>





<a NAME="E1:41"/>
 <a href="pre_topc.html#K2">[#]</a> <font color="Maroon">A</font> <a href="tarski.html#R1">c=</a>  <a href="pre_topc.html#K2">[#]</a> <font color="Maroon">T</font>
 
<b>by </b><i><a class="ref" href="pre_topc.html#D9">PRE_TOPC:def 9</a></i>;<br/>
<b>then reconsider </b><font color="Maroon">At</font> =  <a href="pre_topc.html#K2">[#]</a> <font color="Maroon">A</font> as   <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">T</font> ;<br/>
<b>assume </b><a NAME="E3:41"/><i><font color="Green">E33</font></i>: 
<font color="Maroon">F</font> is <a href="tops_2.html#V1" target="_self">open</a>
 ;<br/>

<b>defpred </b><font color="Maroon">S<sub>1</sub></font>[  <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">T</font>] <b>means </b> ex <font color="Olive">X1</font> being  <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">T</font> st <br/>( <font color="Olive">X1</font> <a href="hidden.html#R1">=</a> <font color="Maroon">a<sub>1</sub></font> &amp; <font color="Olive">X1</font> is <a href="pre_topc.html#V3">open</a> &amp; <font color="Maroon">a<sub>1</sub></font> <a href="subset_1.html#K9">/\</a> <font color="Maroon">At</font> <a href="hidden.html#R2">in</a> <font color="Maroon">F</font> );<br/>
<b>consider </b><font color="Maroon">G</font> being   <a href="struct_0.html#NM3">Subset-Family</a> of <font color="Maroon">T</font><b> such that </b><br/><a NAME="E5:41"/><i><font color="Green">E34</font></i>: 
for <font color="Olive">X</font> being  <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">T</font> holds <br/> ( <font color="Olive">X</font> <a href="hidden.html#R2">in</a> <font color="Maroon">G</font> iff <font color="Maroon">S<sub>1</sub></font>[<font color="Olive">X</font>] )
 <b>from </b><i><a class="ref" href="subset_1.html#S3">SUBSET_1:sch 3</a>();<br/></i>
<b>take </b>
<font color="Maroon">G</font>
;<br/>

<b>thus </b><a NAME="E6:41"/>
<font color="Maroon">G</font> is <a href="tops_2.html#V1" target="_self">open</a>
 <div><a class="txt" onclick="hs2(this)" href="javascript:()" title="41_1"><b>proof </b></a><div class="add">

<b>let </b><font color="Maroon">H</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="tops_2.html#D1" target="_self">TOPS_2:def 1</a><br/>

<b>assume </b><a NAME="E1:41_1"/>
<font color="Maroon">H</font> <a href="hidden.html#R2">in</a> <font color="Maroon">G</font>
 ;<br/>

<a NAME="E2:41_1"/><b>then </b>
 ex <font color="Olive">X1</font> being  <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">T</font> st <br/>( <font color="Olive">X1</font> <a href="hidden.html#R1">=</a> <font color="Maroon">H</font> &amp; <font color="Olive">X1</font> is <a href="pre_topc.html#V3">open</a> &amp; <font color="Maroon">H</font> <a href="subset_1.html#K9">/\</a> <font color="Maroon">At</font> <a href="hidden.html#R2">in</a> <font color="Maroon">F</font> )
 
<b>by </b><i/>;<br/>
<b>hence </b><a NAME="E3:41_1"/>
<font color="Maroon">H</font> is <a href="pre_topc.html#V3">open</a>
 ;<br/>


</div><b>end;</b></div>

<b>let </b><font color="Maroon">AA</font> be   <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">T</font>;<br/>

<b>assume </b><a NAME="E7:41"/><i><font color="Green">E40</font></i>: 
<font color="Maroon">AA</font> <a href="hidden.html#R1">=</a>  <a href="pre_topc.html#K2">[#]</a> <font color="Maroon">A</font>
 ;<br/>

<a NAME="E8:41"/><b>then </b>
<font color="Maroon">F</font> <a href="tarski.html#R1">c=</a>  <a href="zfmisc_1.html#K1">bool</a> <font color="Maroon">AA</font>
 
;<br/>
<a NAME="E9:41"/><b>then </b>
<font color="Maroon">F</font> <a href="tarski.html#R1">c=</a>  <a href="zfmisc_1.html#K1">bool</a> <span class="p1">(<span class="default"><a href="pre_topc.html#K2">[#]</a> <span class="p2">(<span class="default"><font color="Maroon">T</font> <a href="pre_topc.html#K3">|</a> <font color="Maroon">AA</font></span>)</span></span>)</span>
 
<b>by </b><i><a class="ref" href="pre_topc.html#D10">PRE_TOPC:def 10</a></i>;<br/>
<b>then reconsider </b><font color="Maroon">FF</font> = <font color="Maroon">F</font> as   <a href="struct_0.html#NM3">Subset-Family</a> of <span class="p1">(<span class="default"><font color="Maroon">T</font> <a href="pre_topc.html#K3">|</a> <font color="Maroon">AA</font></span>)</span> ;<br/>
<a NAME="E11:41"/>
for <font color="Olive">X</font> being  <a href="struct_0.html#NM2">Subset</a> of <span class="p1">(<span class="default"><font color="Maroon">T</font> <a href="pre_topc.html#K3">|</a> <font color="Maroon">AA</font></span>)</span> holds <br/> ( <font color="Olive">X</font> <a href="hidden.html#R2">in</a> <font color="Maroon">FF</font> iff  ex <font color="Olive">X'</font> being  <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">T</font> st <br/>( <font color="Olive">X'</font> <a href="hidden.html#R2">in</a> <font color="Maroon">G</font> &amp; <font color="Olive">X'</font> <a href="subset_1.html#K9">/\</a> <font color="Maroon">AA</font> <a href="hidden.html#R1">=</a> <font color="Olive">X</font> ) )
 
<div><a class="txt" onclick="hs2(this)" href="javascript:()" title="41_2"><b>proof </b></a><div class="add">

<b>let </b><font color="Maroon">X</font> be   <a href="struct_0.html#NM2">Subset</a> of <span class="p1">(<span class="default"><font color="Maroon">T</font> <a href="pre_topc.html#K3">|</a> <font color="Maroon">AA</font></span>)</span>;<br/>

<b>thus </b><a NAME="E1:41_2"/>
( <font color="Maroon">X</font> <a href="hidden.html#R2">in</a> <font color="Maroon">FF</font> implies  ex <font color="Olive">X'</font> being  <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">T</font> st <br/>( <font color="Olive">X'</font> <a href="hidden.html#R2">in</a> <font color="Maroon">G</font> &amp; <font color="Olive">X'</font> <a href="subset_1.html#K9">/\</a> <font color="Maroon">AA</font> <a href="hidden.html#R1">=</a> <font color="Maroon">X</font> ) )
 <div><a class="txt" onclick="hs2(this)" href="javascript:()" title="41_2_1"><b>proof </b></a><div class="add">

<b>assume </b><a NAME="E1:41_2_1"/><i><font color="Green">E41</font></i>: 
<font color="Maroon">X</font> <a href="hidden.html#R2">in</a> <font color="Maroon">FF</font>
 ;<br/>

<b>then reconsider </b><font color="Maroon">XX</font> = <font color="Maroon">X</font> as   <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">A</font> ;<br/>
<a NAME="E3:41_2_1"/>
<font color="Maroon">XX</font> is <a href="pre_topc.html#V3">open</a>
 
<b>by </b><i>, , </i>;<br/>
<b>then consider </b><font color="Maroon">Y</font> being   <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">T</font><b> such that </b><br/><a NAME="E5:41_2_1"/><i><font color="Green">E42</font></i>: 
<font color="Maroon">Y</font> is <a href="pre_topc.html#V3">open</a>
 <b>and </b><br/><a NAME="E6:41_2_1"/><i><font color="Green">E43</font></i>: 
<font color="Maroon">Y</font> <a href="subset_1.html#K9">/\</a> <span class="p1">(<span class="default"><a href="pre_topc.html#K2">[#]</a> <font color="Maroon">A</font></span>)</span> <a href="hidden.html#R1">=</a> <font color="Maroon">XX</font>
 <b>by </b><i/>;<br/>
<b>take </b><font color="Maroon">X'</font> = <font color="Maroon">Y</font>;<br/>

<b>thus </b><a NAME="E7:41_2_1"/>
( <font color="Maroon">X'</font> <a href="hidden.html#R2">in</a> <font color="Maroon">G</font> &amp; <font color="Maroon">X'</font> <a href="subset_1.html#K9">/\</a> <font color="Maroon">AA</font> <a href="hidden.html#R1">=</a> <font color="Maroon">X</font> )
 <b>by </b><i>, , , , </i>;<br/>


</div><b>end;</b></div>

<b>given </b><font color="Maroon">X'</font> being   <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">T</font><b> such that </b><a NAME="E2:41_2"/><i><font color="Green">E45</font></i>: 
( <font color="Maroon">X'</font> <a href="hidden.html#R2">in</a> <font color="Maroon">G</font> &amp; <font color="Maroon">X'</font> <a href="subset_1.html#K9">/\</a> <font color="Maroon">AA</font> <a href="hidden.html#R1">=</a> <font color="Maroon">X</font> )
 ;<br/>

<a NAME="E3:41_2"/>
 ex <font color="Olive">X1</font> being  <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">T</font> st <br/>( <font color="Olive">X1</font> <a href="hidden.html#R1">=</a> <font color="Maroon">X'</font> &amp; <font color="Olive">X1</font> is <a href="pre_topc.html#V3">open</a> &amp; <font color="Maroon">X'</font> <a href="subset_1.html#K9">/\</a> <font color="Maroon">At</font> <a href="hidden.html#R2">in</a> <font color="Maroon">F</font> )
 
<b>by </b><i>, </i>;<br/>
<b>hence </b><a NAME="E4:41_2"/>
<font color="Maroon">X</font> <a href="hidden.html#R2">in</a> <font color="Maroon">FF</font>
 <b>by </b><i>, </i>;<br/>


</div><b>end;</b></div>
<b>hence </b><a NAME="E12:41"/>
<font color="Maroon">F</font> <a href="hidden.html#R1">=</a> <font color="Maroon">G</font> <a href="tops_2.html#K1" target="_self">|</a> <font color="Maroon">AA</font>
 <b>by </b><i/>;<br/>


</div>
