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<b>let </b><font color="Maroon" title="c1">G</font> be   <a href="incproj.html#NM2" title="INCPROJ:NM.2">IncProjSp</a>;<br/><b>let </b><font color="Maroon" title="c2">a</font>, <font color="Maroon" title="c3">b</font>, <font color="Maroon" title="c4">c</font> be   <a href="incsp_1.html#NM1" title="INCSP_1:NM.1">POINT</a> of <font color="Maroon" title="c1">G</font>;<br/>







<b>assume </b><b>that </b><br/><a NAME="E1:36"/><i><font color="Green" title="E32">A1</font></i>: 
<font color="Maroon" title="c2">a</font>,<font color="Maroon" title="c3">b</font>,<font color="Maroon" title="c4">c</font> <a href="projpl_1.html#NR6" title="PROJPL_1:NR.6">is_a_triangle</a> 
 <b>and </b><br/><a NAME="E2:36"/><i><font color="Green" title="E33">A2</font></i>: 
not <font color="Maroon" title="c2">a</font>,<font color="Maroon" title="c3">b</font>,<font color="Maroon" title="c4">c</font> <a href="zfmisc_1.html#R1" title="ZFMISC_1:pred.1">are_mutually_different</a> 
 ;<br/>

<div><a class="txt" onclick="hs2(this)" href="javascript:()" title="36_1"><b>now </b></a><div class="add"><div><a class="txt" onclick="hsNdiv(this)" href="javascript:()" title="36_1_1"><b>per </b></a><a class="txt" onclick="hs(this)" href="javascript:()"><b>cases </b></a><span class="hide"><a NAME="E1:36_1_1"/>
( <font color="Maroon" title="c2">a</font> <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a> <font color="Maroon" title="c3">b</font> or <font color="Maroon" title="c3">b</font> <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a> <font color="Maroon" title="c4">c</font> or <font color="Maroon" title="c4">c</font> <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a> <font color="Maroon" title="c2">a</font> )
 </span><b>by </b><i><a class="txt" href="projpl_1.html#E2:36"><i><font color="Green" title="E33">A2</font></i></a>, <a class="ref" href="zfmisc_1.html#D5" title="ZFMISC_1:def.5">ZFMISC_1:def 5</a></i>;<br/><div class="add"><div><a class="txt" onclick="hsNdiv(this)" href="javascript:()" title="36_1_1_1"><b>case </b></a><a NAME="E1:36_1_1_1"/><i><font color="Green" title="E34">A3</font></i>: 
<font color="Maroon" title="c2">a</font> <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a> <font color="Maroon" title="c3">b</font>
 ;<br/><div class="add"><b>consider </b><font color="Maroon" title="c5">P</font> being   <a href="incsp_1.html#NM2" title="INCSP_1:NM.2">LINE</a> of <font color="Maroon" title="c1">G</font><b> such that </b><br/><a NAME="E3:36_1_1_1"/><i><font color="Green" title="E35">A4</font></i>: 
( <font color="Maroon" title="c3">b</font> <a href="incsp_1.html#R1" title="INCSP_1:pred.1">on</a> <font color="Maroon" title="c5">P</font> &amp; <font color="Maroon" title="c4">c</font> <a href="incsp_1.html#R1" title="INCSP_1:pred.1">on</a> <font color="Maroon" title="c5">P</font> )
 <b>by </b><i><a class="ref" href="incproj.html#D10" title="INCPROJ:def.10">INCPROJ:def 10</a></i>;<br/><b>thus </b><a NAME="E4:36_1_1_1"/>
contradiction
 <b>by </b><i><a class="txt" href="projpl_1.html#E1:36"><i><font color="Green" title="E32">A1</font></i></a>, <a class="txt" href="projpl_1.html#E1:36_1_1_1"><i><font color="Green" title="E34">A3</font></i></a>, <a class="txt" href="projpl_1.html#E3:36_1_1_1"><i><font color="Green" title="E35">A4</font></i></a>, <a class="ref" href="projpl_1.html#T5" target="_self" title="PROJPL_1:th.5">Th5</a></i>;<br/></div><b>end;</b></div><div><a class="txt" onclick="hsNdiv(this)" href="javascript:()" title="36_1_1_2"><b>case </b></a><a NAME="E1:36_1_1_2"/><i><font color="Green" title="E34">A5</font></i>: 
<font color="Maroon" title="c3">b</font> <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a> <font color="Maroon" title="c4">c</font>
 ;<br/><div class="add"><b>consider </b><font color="Maroon" title="c5">P</font> being   <a href="incsp_1.html#NM2" title="INCSP_1:NM.2">LINE</a> of <font color="Maroon" title="c1">G</font><b> such that </b><br/><a NAME="E3:36_1_1_2"/><i><font color="Green" title="E35">A6</font></i>: 
( <font color="Maroon" title="c2">a</font> <a href="incsp_1.html#R1" title="INCSP_1:pred.1">on</a> <font color="Maroon" title="c5">P</font> &amp; <font color="Maroon" title="c3">b</font> <a href="incsp_1.html#R1" title="INCSP_1:pred.1">on</a> <font color="Maroon" title="c5">P</font> )
 <b>by </b><i><a class="ref" href="incproj.html#D10" title="INCPROJ:def.10">INCPROJ:def 10</a></i>;<br/><b>thus </b><a NAME="E4:36_1_1_2"/>
contradiction
 <b>by </b><i><a class="txt" href="projpl_1.html#E1:36"><i><font color="Green" title="E32">A1</font></i></a>, <a class="txt" href="projpl_1.html#E1:36_1_1_2"><i><font color="Green" title="E34">A5</font></i></a>, <a class="txt" href="projpl_1.html#E3:36_1_1_2"><i><font color="Green" title="E35">A6</font></i></a>, <a class="ref" href="projpl_1.html#T5" target="_self" title="PROJPL_1:th.5">Th5</a></i>;<br/></div><b>end;</b></div><div><a class="txt" onclick="hsNdiv(this)" href="javascript:()" title="36_1_1_3"><b>case </b></a><a NAME="E1:36_1_1_3"/><i><font color="Green" title="E34">A7</font></i>: 
<font color="Maroon" title="c4">c</font> <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a> <font color="Maroon" title="c2">a</font>
 ;<br/><div class="add"><b>consider </b><font color="Maroon" title="c5">P</font> being   <a href="incsp_1.html#NM2" title="INCSP_1:NM.2">LINE</a> of <font color="Maroon" title="c1">G</font><b> such that </b><br/><a NAME="E3:36_1_1_3"/><i><font color="Green" title="E35">A8</font></i>: 
( <font color="Maroon" title="c3">b</font> <a href="incsp_1.html#R1" title="INCSP_1:pred.1">on</a> <font color="Maroon" title="c5">P</font> &amp; <font color="Maroon" title="c4">c</font> <a href="incsp_1.html#R1" title="INCSP_1:pred.1">on</a> <font color="Maroon" title="c5">P</font> )
 <b>by </b><i><a class="ref" href="incproj.html#D10" title="INCPROJ:def.10">INCPROJ:def 10</a></i>;<br/><b>thus </b><a NAME="E4:36_1_1_3"/>
contradiction
 <b>by </b><i><a class="txt" href="projpl_1.html#E1:36"><i><font color="Green" title="E32">A1</font></i></a>, <a class="txt" href="projpl_1.html#E1:36_1_1_3"><i><font color="Green" title="E34">A7</font></i></a>, <a class="txt" href="projpl_1.html#E3:36_1_1_3"><i><font color="Green" title="E35">A8</font></i></a>, <a class="ref" href="projpl_1.html#T5" target="_self" title="PROJPL_1:th.5">Th5</a></i>;<br/></div><b>end;</b></div></div><b>end;</b></div></div><b>end;</b></div>
<b>hence </b><a NAME="E4:36"/>
contradiction
 ;<br/>


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