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<b>let </b><font color="Maroon">CPS</font> be  <a href="collsp.html#V4">proper</a> <a href="collsp.html#NM2">CollSp</a>;<br/>

<b>consider </b><font color="Maroon">a''</font> being   <a href="pre_topc.html#NM2">Point</a> of <font color="Maroon">CPS</font>, <font color="Maroon">b''</font> being   <a href="pre_topc.html#NM2">Point</a> of <font color="Maroon">CPS</font>, <font color="Maroon">c''</font> being   <a href="pre_topc.html#NM2">Point</a> of <font color="Maroon">CPS</font><b> such that </b><br/><a NAME="E2:9"/><i><font color="Green">E21</font></i>: 
not <font color="Maroon">a''</font>,<font color="Maroon">b''</font>,<font color="Maroon">c''</font> <a href="collsp.html#R1">is_collinear</a> 
 <b>by </b><i><a class="ref" href="collsp.html#D6">COLLSP:def 6</a></i>;<br/>
<a NAME="E3:9"/>
( <font color="Maroon">a''</font> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a> <font color="Maroon">b''</font> &amp; <font color="Maroon">b''</font> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a> <font color="Maroon">c''</font> &amp; <font color="Maroon">c''</font> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a> <font color="Maroon">a''</font> )
 
<b>by </b><i>, <a class="ref" href="collsp.html#T7">COLLSP:7</a></i>;<br/>
<b>hence </b><a NAME="E4:9"/>
 ex <font color="Olive">a'</font>, <font color="Olive">b'</font>, <font color="Olive">c'</font> being  <a href="pre_topc.html#NM2">Point</a> of <font color="Maroon">CPS</font> st <br/>( <font color="Olive">a'</font> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a> <font color="Olive">b'</font> &amp; <font color="Olive">b'</font> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a> <font color="Olive">c'</font> &amp; <font color="Olive">c'</font> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a> <font color="Olive">a'</font> )
 ;<br/>


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