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<b>consider </b><font color="Maroon">y</font> being   <a href="struct_0.html#NM1">Element</a> of <font color="Maroon">M</font>;<br/>
<a NAME="E2:23_1_1"/>
<font color="Maroon">y</font> <a href="metric_2.html#K1" target="_self">-neighbour</a>  <a href="hidden.html#R2">in</a> <span class="p1">{<span class="default"> <font color="Olive">s</font> where <font color="Olive">s</font> is   <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">M</font> :  ex <font color="Olive">x</font> being  <a href="struct_0.html#NM1">Element</a> of <font color="Maroon">M</font> st <font color="Olive">x</font> <a href="metric_2.html#K1" target="_self">-neighbour</a>  <a href="hidden.html#R1">=</a> <font color="Olive">s</font> </span>}</span> 
 
;<br/>
<b>hence </b><a NAME="E3:23_1_1"/>
not <font color="Maroon">M</font> <a href="metric_2.html#K2" target="_self">-neighbour</a>  is <a href="xboole_0.html#V1">empty</a>
 ;<br/>


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