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<b>let </b><font color="Maroon">S</font> be   <a href="incsp_1.html#NM4">IncSpace</a>;<br/><b>let </b><font color="Maroon">A</font> be   <a href="incsp_1.html#NM1">POINT</a> of <font color="Maroon">S</font>;<br/><b>let </b><font color="Maroon">B</font> be   <a href="incsp_1.html#NM1">POINT</a> of <font color="Maroon">S</font>;<br/><b>let </b><font color="Maroon">C</font> be   <a href="incsp_1.html#NM1">POINT</a> of <font color="Maroon">S</font>;<br/><b>let </b><font color="Maroon">D</font> be   <a href="incsp_1.html#NM1">POINT</a> of <font color="Maroon">S</font>;<br/>









<b>assume </b><a NAME="E1:60"/>
( not <span class="p1"><a href="domain_1.html#K8">{</a><span class="default"><font color="Maroon">A</font>,<font color="Maroon">B</font>,<font color="Maroon">C</font></span><a href="domain_1.html#K8">}</a></span> <a href="incsp_1.html#NR6" target="_self">is_collinear</a>  &amp; <font color="Maroon">D</font> <a href="incsp_1.html#R2" target="_self">on</a>  <a href="incsp_1.html#K2" target="_self">Plane</a> <font color="Maroon">A</font>,<font color="Maroon">B</font>,<font color="Maroon">C</font> )
 ;<br/>

<a NAME="E2:60"/><b>then </b>
( <span class="p1"><a href="domain_1.html#K8">{</a><span class="default"><font color="Maroon">A</font>,<font color="Maroon">B</font>,<font color="Maroon">C</font></span><a href="domain_1.html#K8">}</a></span> <a href="incsp_1.html#R5" target="_self">on</a>  <a href="incsp_1.html#K2" target="_self">Plane</a> <font color="Maroon">A</font>,<font color="Maroon">B</font>,<font color="Maroon">C</font> &amp; <font color="Maroon">D</font> <a href="incsp_1.html#R2" target="_self">on</a>  <a href="incsp_1.html#K2" target="_self">Plane</a> <font color="Maroon">A</font>,<font color="Maroon">B</font>,<font color="Maroon">C</font> )
 
<b>by </b><i><a class="ref" href="incsp_1.html#T18" target="_self">Th18</a></i>;<br/>
<a NAME="E3:60"/><b>then </b>
<span class="p1"><a href="domain_1.html#K8">{</a><span class="default"><font color="Maroon">A</font>,<font color="Maroon">B</font>,<font color="Maroon">C</font></span><a href="domain_1.html#K8">}</a></span> <a href="subset_1.html#K4">\/</a> <span class="p1"><a href="domain_1.html#K6">{</a><span class="default"><font color="Maroon">D</font></span><a href="domain_1.html#K6">}</a></span> <a href="incsp_1.html#R5" target="_self">on</a>  <a href="incsp_1.html#K2" target="_self">Plane</a> <font color="Maroon">A</font>,<font color="Maroon">B</font>,<font color="Maroon">C</font>
 
<b>by </b><i><a class="ref" href="incsp_1.html#D2" target="_self">Def2</a></i>;<br/>
<a NAME="E4:60"/><b>then </b>
<span class="p1"><a href="domain_1.html#K9">{</a><span class="default"><font color="Maroon">A</font>,<font color="Maroon">B</font>,<font color="Maroon">C</font>,<font color="Maroon">D</font></span><a href="domain_1.html#K9">}</a></span> <a href="incsp_1.html#R5" target="_self">on</a>  <a href="incsp_1.html#K2" target="_self">Plane</a> <font color="Maroon">A</font>,<font color="Maroon">B</font>,<font color="Maroon">C</font>
 
<b>by </b><i><a class="ref" href="enumset1.html#T46">ENUMSET1:46</a></i>;<br/>
<b>hence </b><a NAME="E5:60"/>
<span class="p1"><a href="domain_1.html#K9">{</a><span class="default"><font color="Maroon">A</font>,<font color="Maroon">B</font>,<font color="Maroon">C</font>,<font color="Maroon">D</font></span><a href="domain_1.html#K9">}</a></span> <a href="incsp_1.html#NR7" target="_self">is_coplanar</a> 
 <b>by </b><i/>;<br/>


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