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<b>let </b><font color="Maroon">X</font> be   <a href="subset_1.html#NM2">Subset</a> of <a href="numbers.html#K1">REAL</a> ;<br/>

<a NAME="E1:30"/>
 <a href="pscomp_1.html#K4" target="_self">-</a> <span class="p1">(<span class="default"><a href="pscomp_1.html#K4" target="_self">-</a> <font color="Maroon">X</font></span>)</span> <a href="hidden.html#R1">=</a> <font color="Maroon">X</font>
 
;<br/>
<b>hence </b><a NAME="E2:30"/>
( <font color="Maroon">X</font> is <a href="rcomp_1.html#V2">closed</a> iff  <a href="pscomp_1.html#K4" target="_self">-</a> <font color="Maroon">X</font> is <a href="rcomp_1.html#V2">closed</a> )
 <b>by </b><i/>;<br/>


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