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<b>let </b><font color="Maroon">A</font> be   <a href="subset_1.html#NM2">Subset</a> of <a href="numbers.html#K1">REAL</a> ;<br/><b>let </b><font color="Maroon">B</font> be   <a href="struct_0.html#NM2">Subset</a> of <a href="topmetr.html#K3">R^1</a> ;<br/>



<b>assume </b><a NAME="E1:68"/><i><font color="Green">E34</font></i>: 
<font color="Maroon">A</font> <a href="hidden.html#R1">=</a> <font color="Maroon">B</font>
 ;<br/>

<div><b>hereby </b>
<div class="add"><b>assume </b><a NAME="E1:68_1"/>
<font color="Maroon">A</font> is <a href="rcomp_1.html#V3">open</a>
 ;<br/><a NAME="E2:68_1"/><b>then </b>
<font color="Maroon">A</font> <a href="hidden.html#R2">in</a>  <a href="pcomps_1.html#K3">Family_open_set</a> <a href="metric_1.html#K8">RealSpace</a> 
 <b>by </b><i><a class="ref" href="jordan5a.html#T6">JORDAN5A:6</a></i>;<br/><a NAME="E3:68_1"/><b>then </b>
<font color="Maroon">A</font> <a href="hidden.html#R2">in</a> the <a href="pre_topc.html#U1">topology</a> of <span class="p1">(<span class="default"><a href="pcomps_1.html#K4">TopSpaceMetr</a> <a href="metric_1.html#K8">RealSpace</a> </span>)</span>
 <b>by </b><i><a class="ref" href="topmetr.html#T16">TOPMETR:16</a></i>;<br/><b>hence </b><a NAME="E4:68_1"/>
<font color="Maroon">B</font> is <a href="pre_topc.html#V3">open</a>
 <b>by </b><i>, <a class="ref" href="pre_topc.html#D5">PRE_TOPC:def 5</a>, <a class="ref" href="topmetr.html#D7">TOPMETR:def 7</a></i>;<br/></div>
<b>end;</b></div>

<b>assume </b><a NAME="E3:68"/>
<font color="Maroon">B</font> is <a href="pre_topc.html#V3">open</a>
 ;<br/>

<a NAME="E4:68"/><b>then </b>
<font color="Maroon">B</font> <a href="hidden.html#R2">in</a> the <a href="pre_topc.html#U1">topology</a> of <a href="topmetr.html#K3">R^1</a> 
 
<b>by </b><i><a class="ref" href="pre_topc.html#D5">PRE_TOPC:def 5</a></i>;<br/>
<a NAME="E5:68"/><b>then </b>
<font color="Maroon">A</font> <a href="hidden.html#R2">in</a>  <a href="pcomps_1.html#K3">Family_open_set</a> <a href="metric_1.html#K8">RealSpace</a> 
 
<b>by </b><i>, <a class="ref" href="topmetr.html#T16">TOPMETR:16</a>, <a class="ref" href="topmetr.html#D7">TOPMETR:def 7</a></i>;<br/>
<b>hence </b><a NAME="E6:68"/>
<font color="Maroon">A</font> is <a href="rcomp_1.html#V3">open</a>
 <b>by </b><i><a class="ref" href="jordan5a.html#T6">JORDAN5A:6</a></i>;<br/>


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