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<b>assume </b><a NAME="E1:31_1_1"/>
not  <a href="graph_3.html#K2" target="_self">Edges_In</a> <font color="Maroon">c<sub>2</sub></font>,<font color="Maroon">c<sub>3</sub></font> is <a href="xboole_0.html#V1">empty</a>
 ;<br/>

<b>then consider </b><font color="Maroon">c<sub>4</sub></font> being    <a href="hidden.html#M1">set</a> <b> such that </b><br/><a NAME="E3:31_1_1"/><i><font color="Green">E24</font></i>: 
<font color="Maroon">c<sub>4</sub></font> <a href="hidden.html#R2">in</a>  <a href="graph_3.html#K2" target="_self">Edges_In</a> <font color="Maroon">c<sub>2</sub></font>,<font color="Maroon">c<sub>3</sub></font>
 <b>by </b><i><a class="ref" href="xboole_0.html#D1">XBOOLE_0:def 1</a></i>;<br/>
<b>thus </b><a NAME="E4:31_1_1"/>
contradiction
 <b>by </b><i><a class="txt" href="graph_3.html#E3:31_1_1"><i><font color="Green">E24</font></i></a>, <a class="ref" href="graph_3.html#D1" target="_self">Def1</a></i>;<br/>


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