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<b>let </b><font color="Maroon" title="c1">A</font> be   <a href="struct_0.html#NM2" title="STRUCT_0:NM.2">Subset</a> of <a href="topmetr.html#K3" title="TOPMETR:func.3">R^1</a> ;<br/><b>let </b><font color="Maroon" title="c2">a</font> be  <a href="xreal_0.html#V1" title="XREAL_0:attr.1">real</a>  <a href="ordinal1.html#NM1" title="ORDINAL1:NM.1">number</a> ;<br/>



<b>assume </b><a NAME="E1:69"/><i><font color="Green" title="E57">A1</font></i>: 
<font color="Maroon" title="c1">A</font> <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a> <span class="p1"><a href="borsuk_5.html#NK4" title="BORSUK_5:NK.4">].</a><span class="default"><font color="Maroon" title="c2">a</font></span><a href="borsuk_5.html#NK4" title="BORSUK_5:NK.4">,+infty.[</a></span>
 ;<br/>

<a NAME="E2:69"/>
<span class="p1"><a href="borsuk_5.html#NK4" title="BORSUK_5:NK.4">].</a><span class="default"><font color="Maroon" title="c2">a</font></span><a href="borsuk_5.html#NK4" title="BORSUK_5:NK.4">,+infty.[</a></span> is <a href="rcomp_1.html#V3" title="RCOMP_1:attr.3">open</a>
 
<b>by </b><i><a class="txt" href="borsuk_5.html#E78"><i><font color="Green" title="E52">Lm11</font></i></a></i>;<br/>
<b>hence </b><a NAME="E3:69"/>
<font color="Maroon" title="c1">A</font> is <a href="pre_topc.html#V3" title="PRE_TOPC:attr.3">open</a>
 <b>by </b><i><a class="txt" href="borsuk_5.html#E1:69"><i><font color="Green" title="E57">A1</font></i></a>, <a class="ref" href="borsuk_5.html#T62" target="_self" title="BORSUK_5:th.62">Th62</a></i>;<br/>


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