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<b>let </b><font color="Maroon">A</font> be   <a href="struct_0.html#NM2">Subset</a> of <a href="topmetr.html#K3">R^1</a> ;<br/><b>let </b><font color="Maroon">a</font> be  <a href="xreal_0.html#V1">real</a>  <a href="ordinal1.html#NM1" target="_self">number</a> ;<br/>



<b>assume </b><a NAME="E1:70"/><i><font color="Green">E34</font></i>: 
<font color="Maroon">A</font> <a href="hidden.html#R1">=</a> <span class="p1"><a href="borsuk_5.html#NK2" target="_self">].-infty,</a><span class="default"><font color="Maroon">a</font></span><a href="borsuk_5.html#NK2" target="_self">.[</a></span>
 ;<br/>

<a NAME="E2:70"/>
<span class="p1"><a href="borsuk_5.html#NK2" target="_self">].-infty,</a><span class="default"><font color="Maroon">a</font></span><a href="borsuk_5.html#NK2" target="_self">.[</a></span> is <a href="rcomp_1.html#V3">open</a>
 
<b>by </b><i/>;<br/>
<b>hence </b><a NAME="E3:70"/>
<font color="Maroon">A</font> is <a href="pre_topc.html#V3">open</a>
 <b>by </b><i>, <a class="ref" href="borsuk_5.html#T11" target="_self">Th11</a></i>;<br/>


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