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<b>let </b><font color="Maroon">A</font> be    <a href="rcomp_1.html#M1" target="_self">Neighbourhood</a> of <font color="Maroon">r</font>;<br/>

<a NAME="E1:37_1_1"/>
 ex <font color="Olive">g</font> being <a href="xreal_0.html#V1">real</a>  <a href="ordinal1.html#NM1" target="_self">number</a>  st <br/>( 0 <a href="xxreal_0.html#NR3" target="_self">&lt;</a> <font color="Olive">g</font> &amp; <font color="Maroon">A</font> <a href="hidden.html#R1">=</a> <span class="p1"><a href="rcomp_1.html#K2" target="_self">].</a><span class="default"><span class="p2">(<span class="default"><font color="Maroon">r</font> <a href="xcmplx_0.html#K6">-</a> <font color="Olive">g</font></span>)</span>,<span class="p2">(<span class="default"><font color="Maroon">r</font> <a href="xcmplx_0.html#K2">+</a> <font color="Olive">g</font></span>)</span></span><a href="rcomp_1.html#K2" target="_self">.[</a></span> )
 
<b>by </b><i/>;<br/>
<b>hence </b><a NAME="E2:37_1_1"/>
<font color="Maroon">A</font> is <a href="rcomp_1.html#V3" target="_self">open</a>
 ;<br/>


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