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<b>let </b><font color="Maroon">Y</font> be    <a href="pre_topc.html#L1">TopStruct</a> ;<br/><b>let </b><font color="Maroon">Y0</font> be    <a href="tsp_1.html#M2" target="_self">SubSpace</a> of <font color="Maroon">Y</font>;<br/>



<a NAME="E1:4"/>
(  <a href="pre_topc.html#K2">[#]</a> <font color="Maroon">Y0</font> <a href="hidden.html#R1">=</a> the <a href="struct_0.html#U1">carrier</a> of <font color="Maroon">Y0</font> &amp;  <a href="pre_topc.html#K2">[#]</a> <font color="Maroon">Y</font> <a href="hidden.html#R1">=</a> the <a href="struct_0.html#U1">carrier</a> of <font color="Maroon">Y</font> )
 
;<br/>
<b>then reconsider </b><font color="Maroon">A</font> = the <a href="struct_0.html#U1">carrier</a> of <font color="Maroon">Y0</font> as   <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">Y</font> <b>by </b><i><a class="ref" href="pre_topc.html#D9">PRE_TOPC:def 9</a></i>;<br/>
<b>let </b><font color="Maroon">F</font> be   <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">Y</font>;<br/>

<b>reconsider </b><font color="Maroon">F0</font> = <font color="Maroon">F</font> <a href="subset_1.html#K9">/\</a> <font color="Maroon">A</font> as   <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">Y0</font> <b>by </b><i><a class="ref" href="xboole_1.html#T17">XBOOLE_1:17</a></i>;<br/>
<b>assume </b><a NAME="E4:4"/><i><font color="Green">E17</font></i>: 
<font color="Maroon">F</font> is <a href="pre_topc.html#V4">closed</a>
 ;<br/>

<b>take </b>
<font color="Maroon">F0</font>
;<br/>

<b>thus </b><a NAME="E5:4"/>
<font color="Maroon">F0</font> is <a href="pre_topc.html#V4">closed</a>
 <b>by </b><i>, </i>;<br/>

<b>thus </b><a NAME="E6:4"/>
<font color="Maroon">F0</font> <a href="hidden.html#R1">=</a> <font color="Maroon">F</font> <a href="subset_1.html#K8">/\</a> the <a href="struct_0.html#U1">carrier</a> of <font color="Maroon">Y0</font>
 ;<br/>


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