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<b>take </b><font color="Maroon" title="c2">B</font> = the <a href="pre_topc.html#U1" title="PRE_TOPC:sel.1">topology</a> of <font color="Maroon" title="c1">T</font>;<br/>

<b>thus </b><a NAME="E1:18_1_1"/>
( <font color="Maroon" title="c2">B</font> is <a href="tops_2.html#V1" title="TOPS_2:attr.1">open</a> &amp; not <font color="Maroon" title="c2">B</font> is <a href="xboole_0.html#V1" title="XBOOLE_0:attr.1">empty</a> )
 <b>by </b><i><a class="ref" href="cantor_1.html#T3" title="CANTOR_1:th.3">CANTOR_1:3</a></i>;<br/>


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