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<b>let </b><font color="Maroon">G</font> be    <a href="incsp_1.html#L1">IncProjStr</a> ;<br/>

<b>assume </b><a NAME="E1:22"/><i><font color="Green">E36</font></i>: 
<font color="Maroon">G</font> is   <a href="incproj.html#NM2">IncProjSp</a>
 ;<br/>

<b>then consider </b><font color="Maroon">A</font> being   <a href="incsp_1.html#NM2">LINE</a> of <font color="Maroon">G</font>, <font color="Maroon">B</font> being   <a href="incsp_1.html#NM2">LINE</a> of <font color="Maroon">G</font><b> such that </b><br/><a NAME="E3:22"/><i><font color="Green">E37</font></i>: 
<font color="Maroon">A</font> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a> <font color="Maroon">B</font>
 <b>by </b><i/>;<br/>
<b>consider </b><font color="Maroon">a</font> being   <a href="incsp_1.html#NM1">POINT</a> of <font color="Maroon">G</font>, <font color="Maroon">b</font> being   <a href="incsp_1.html#NM1">POINT</a> of <font color="Maroon">G</font><b> such that </b><br/><a NAME="E5:22"/><i><font color="Green">E40</font></i>: 
( <font color="Maroon">a</font> <a href="incsp_1.html#R1">on</a> <font color="Maroon">A</font> &amp; <font color="Maroon">a</font> <a href="projpl_1.html#NR1" target="_self">|'</a> <font color="Maroon">B</font> &amp; <font color="Maroon">b</font> <a href="incsp_1.html#R1">on</a> <font color="Maroon">B</font> &amp; <font color="Maroon">b</font> <a href="projpl_1.html#NR1" target="_self">|'</a> <font color="Maroon">A</font> )
 <b>by </b><i>, , <a class="ref" href="projred1.html#T3">PROJRED1:3</a></i>;<br/>
<b>consider </b><font color="Maroon">p</font> being   <a href="incsp_1.html#NM1">POINT</a> of <font color="Maroon">G</font><b> such that </b><br/><a NAME="E7:22"/><i><font color="Green">E41</font></i>: 
( <font color="Maroon">p</font> <a href="incsp_1.html#R1">on</a> <font color="Maroon">A</font> &amp; <font color="Maroon">p</font> <a href="projpl_1.html#NR1" target="_self">|'</a> <font color="Maroon">B</font> &amp; <font color="Maroon">a</font> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a> <font color="Maroon">p</font> )
 <b>by </b><i>, , </i>;<br/>
<b>consider </b><font color="Maroon">q</font> being   <a href="incsp_1.html#NM1">POINT</a> of <font color="Maroon">G</font><b> such that </b><br/><a NAME="E9:22"/><i><font color="Green">E42</font></i>: 
( <font color="Maroon">q</font> <a href="incsp_1.html#R1">on</a> <font color="Maroon">B</font> &amp; <font color="Maroon">q</font> <a href="projpl_1.html#NR1" target="_self">|'</a> <font color="Maroon">A</font> &amp; <font color="Maroon">b</font> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a> <font color="Maroon">q</font> )
 <b>by </b><i>, , </i>;<br/>
<a NAME="E10:22"/><i><font color="Green">E43</font></i>: 
<font color="Maroon">G</font> is <a href="projpl_1.html#V1" target="_self">configuration</a>
 
<b>by </b><i>, </i>;<br/>
<b>take </b>
<font color="Maroon">a</font>
;<br/>

<b>take </b>
<font color="Maroon">p</font>
;<br/>

<b>take </b>
<font color="Maroon">b</font>
;<br/>

<b>take </b>
<font color="Maroon">q</font>
;<br/>

<a NAME="E11:22"/><i><font color="Green">E44</font></i>: 
( <font color="Maroon">a</font>,<font color="Maroon">p</font> <a href="incproj.html#R3">on</a> <font color="Maroon">A</font> &amp; <font color="Maroon">b</font>,<font color="Maroon">q</font> <a href="incproj.html#R3">on</a> <font color="Maroon">B</font> )
 
<b>by </b><i>, , , <a class="ref" href="incproj.html#D7">INCPROJ:def 7</a></i>;<br/>
<a NAME="E12:22"/>
( <font color="Maroon">a</font>,<font color="Maroon">p</font> <a href="projpl_1.html#R1" target="_self">|'</a> <font color="Maroon">B</font> &amp; <font color="Maroon">b</font>,<font color="Maroon">q</font> <a href="projpl_1.html#R1" target="_self">|'</a> <font color="Maroon">A</font> )
 
<b>by </b><i>, , , </i>;<br/>
<b>hence </b><a NAME="E13:22"/>
<font color="Maroon">a</font>,<font color="Maroon">p</font>,<font color="Maroon">b</font>,<font color="Maroon">q</font> <a href="projpl_1.html#R5" target="_self">is_a_quadrangle</a> 
 <b>by </b><i>, , , , </i>;<br/>


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