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<b>let </b><font color="Maroon">X0</font> be    <a href="pre_topc.html#M1">SubSpace</a> of <font color="Maroon">X</font>;<br/>

<b>assume </b><a NAME="E1:41_1_1"/><i><font color="Green">E21</font></i>: 
<font color="Maroon">X0</font> is <a href="tsep_1.html#V1">open</a>
 ;<br/>

<b>let </b><font color="Maroon">A</font> be   <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">X</font>; <i><font color="Red">:: according to </font></i><a class="ref" href="borsuk_1.html#D14">BORSUK_1:def 14</a><br/>

<b>assume </b><a NAME="E2:41_1_1"/>
<font color="Maroon">A</font> <a href="hidden.html#R1">=</a> the <a href="struct_0.html#U1">carrier</a> of <font color="Maroon">X0</font>
 ;<br/>

<a NAME="E3:41_1_1"/><b>then </b>
<font color="Maroon">A</font> is <a href="pre_topc.html#V3">open</a>
 
<b>by </b><i><a class="txt" href="tdlat_3.html#E1:41_1_1"><i><font color="Green">E21</font></i></a>, <a class="ref" href="tsep_1.html#D1">TSEP_1:def 1</a></i>;<br/>
<b>hence </b><a NAME="E4:41_1_1"/>
<font color="Maroon">A</font> is <a href="pre_topc.html#V4">closed</a>
 <b>by </b><i/>;<br/>


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