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<a NAME="E1:61_4_1"/>
 <a href="topreal1.html#K9" target="_self">west_halfline</a> <font color="Maroon">p</font> <a href="hidden.html#R1">=</a> <span class="p1">{<span class="default"> <span class="p2"><a href="euclid.html#K23">|[</a><span class="default"><font color="Olive">r</font>,<span class="p3">(<span class="default"><font color="Maroon">p</font> <a href="euclid.html#K22">`2</a> </span>)</span></span><a href="euclid.html#K23">]|</a></span> where <font color="Olive">r</font> is    <a href="subset_1.html#M1">Element</a> of  <a href="numbers.html#K1">REAL</a>  : <font color="Olive">r</font> <a href="xxreal_0.html#R1">&lt;=</a> <font color="Maroon">p</font> <a href="euclid.html#K21">`1</a>  </span>}</span> 
 
<b>by </b><i/>;<br/>
<a NAME="E2:61_4_1"/><b>then </b>
<span class="p1"><a href="euclid.html#K23">|[</a><span class="default"><span class="p2">(<span class="default"><font color="Maroon">p</font> <a href="euclid.html#K21">`1</a> </span>)</span>,<span class="p2">(<span class="default"><font color="Maroon">p</font> <a href="euclid.html#K22">`2</a> </span>)</span></span><a href="euclid.html#K23">]|</a></span> <a href="hidden.html#R2">in</a>  <a href="topreal1.html#K9" target="_self">west_halfline</a> <font color="Maroon">p</font>
 
;<br/>
<b>hence </b><a NAME="E3:61_4_1"/>
not  <a href="topreal1.html#K9" target="_self">west_halfline</a> <font color="Maroon">p</font> is <a href="xboole_0.html#V1">empty</a>
 ;<br/>


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