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<b>let </b><font color="Maroon">c<sub>1</sub></font> be    <a href="incsp_1.html#L1">IncProjStr</a> ;<br/>

<b>assume </b><a NAME="E1:22"/><i><font color="Green">E20</font></i>: 
<font color="Maroon">c<sub>1</sub></font> is   <a href="incproj.html#NM2">IncProjSp</a>
 ;<br/>

<b>then consider </b><font color="Maroon">c<sub>2</sub></font>, <font color="Maroon">c<sub>3</sub></font> being   <a href="incsp_1.html#NM2">LINE</a> of <font color="Maroon">c<sub>1</sub></font><b> such that </b><br/><a NAME="E3:22"/><i><font color="Green">E21</font></i>: 
<font color="Maroon">c<sub>2</sub></font> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a> <font color="Maroon">c<sub>3</sub></font>
 <b>by </b><i><a class="ref" href="projpl_1.html#T7" target="_self">Th7</a></i>;<br/>
<b>consider </b><font color="Maroon">c<sub>4</sub></font>, <font color="Maroon">c<sub>5</sub></font> being   <a href="incsp_1.html#NM1">POINT</a> of <font color="Maroon">c<sub>1</sub></font><b> such that </b><br/><a NAME="E5:22"/><i><font color="Green">E22</font></i>: 
( <font color="Maroon">c<sub>4</sub></font> <a href="incsp_1.html#R1">on</a> <font color="Maroon">c<sub>2</sub></font> &amp; <font color="Maroon">c<sub>4</sub></font> <a href="projpl_1.html#NR1" target="_self">|'</a> <font color="Maroon">c<sub>3</sub></font> &amp; <font color="Maroon">c<sub>5</sub></font> <a href="incsp_1.html#R1">on</a> <font color="Maroon">c<sub>3</sub></font> &amp; <font color="Maroon">c<sub>5</sub></font> <a href="projpl_1.html#NR1" target="_self">|'</a> <font color="Maroon">c<sub>2</sub></font> )
 <b>by </b><i><a class="txt" href="projpl_1.html#E1:22"><i><font color="Green">E20</font></i></a>, <a class="txt" href="projpl_1.html#E3:22"><i><font color="Green">E21</font></i></a>, <a class="ref" href="projred1.html#T3">PROJRED1:3</a></i>;<br/>
<b>consider </b><font color="Maroon">c<sub>6</sub></font> being   <a href="incsp_1.html#NM1">POINT</a> of <font color="Maroon">c<sub>1</sub></font><b> such that </b><br/><a NAME="E7:22"/><i><font color="Green">E23</font></i>: 
( <font color="Maroon">c<sub>6</sub></font> <a href="incsp_1.html#R1">on</a> <font color="Maroon">c<sub>2</sub></font> &amp; <font color="Maroon">c<sub>6</sub></font> <a href="projpl_1.html#NR1" target="_self">|'</a> <font color="Maroon">c<sub>3</sub></font> &amp; <font color="Maroon">c<sub>4</sub></font> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a> <font color="Maroon">c<sub>6</sub></font> )
 <b>by </b><i><a class="txt" href="projpl_1.html#E1:22"><i><font color="Green">E20</font></i></a>, <a class="txt" href="projpl_1.html#E5:22"><i><font color="Green">E22</font></i></a>, <a class="ref" href="projpl_1.html#T9" target="_self">Th9</a></i>;<br/>
<b>consider </b><font color="Maroon">c<sub>7</sub></font> being   <a href="incsp_1.html#NM1">POINT</a> of <font color="Maroon">c<sub>1</sub></font><b> such that </b><br/><a NAME="E9:22"/><i><font color="Green">E24</font></i>: 
( <font color="Maroon">c<sub>7</sub></font> <a href="incsp_1.html#R1">on</a> <font color="Maroon">c<sub>3</sub></font> &amp; <font color="Maroon">c<sub>7</sub></font> <a href="projpl_1.html#NR1" target="_self">|'</a> <font color="Maroon">c<sub>2</sub></font> &amp; <font color="Maroon">c<sub>5</sub></font> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a> <font color="Maroon">c<sub>7</sub></font> )
 <b>by </b><i><a class="txt" href="projpl_1.html#E1:22"><i><font color="Green">E20</font></i></a>, <a class="txt" href="projpl_1.html#E5:22"><i><font color="Green">E22</font></i></a>, <a class="ref" href="projpl_1.html#T9" target="_self">Th9</a></i>;<br/>
<a NAME="E10:22"/><i><font color="Green">E25</font></i>: 
<font color="Maroon">c<sub>1</sub></font> is <a href="projpl_1.html#V1" target="_self">configuration</a>
 
<b>by </b><i><a class="txt" href="projpl_1.html#E1:22"><i><font color="Green">E20</font></i></a>, <a class="ref" href="projpl_1.html#T4" target="_self">Th4</a></i>;<br/>
<b>take </b>
<font color="Maroon">c<sub>4</sub></font>
;<br/>

<b>take </b>
<font color="Maroon">c<sub>6</sub></font>
;<br/>

<b>take </b>
<font color="Maroon">c<sub>5</sub></font>
;<br/>

<b>take </b>
<font color="Maroon">c<sub>7</sub></font>
;<br/>

<a NAME="E11:22"/><i><font color="Green">E26</font></i>: 
( <font color="Maroon">c<sub>4</sub></font>,<font color="Maroon">c<sub>6</sub></font> <a href="incproj.html#R3">on</a> <font color="Maroon">c<sub>2</sub></font> &amp; <font color="Maroon">c<sub>5</sub></font>,<font color="Maroon">c<sub>7</sub></font> <a href="incproj.html#R3">on</a> <font color="Maroon">c<sub>3</sub></font> )
 
<b>by </b><i><a class="txt" href="projpl_1.html#E5:22"><i><font color="Green">E22</font></i></a>, <a class="txt" href="projpl_1.html#E7:22"><i><font color="Green">E23</font></i></a>, <a class="txt" href="projpl_1.html#E9:22"><i><font color="Green">E24</font></i></a>, <a class="ref" href="incproj.html#D7">INCPROJ:def 7</a></i>;<br/>
<a NAME="E12:22"/>
( <font color="Maroon">c<sub>4</sub></font>,<font color="Maroon">c<sub>6</sub></font> <a href="projpl_1.html#R1" target="_self">|'</a> <font color="Maroon">c<sub>3</sub></font> &amp; <font color="Maroon">c<sub>5</sub></font>,<font color="Maroon">c<sub>7</sub></font> <a href="projpl_1.html#R1" target="_self">|'</a> <font color="Maroon">c<sub>2</sub></font> )
 
<b>by </b><i><a class="txt" href="projpl_1.html#E5:22"><i><font color="Green">E22</font></i></a>, <a class="txt" href="projpl_1.html#E7:22"><i><font color="Green">E23</font></i></a>, <a class="txt" href="projpl_1.html#E9:22"><i><font color="Green">E24</font></i></a>, <a class="ref" href="projpl_1.html#D1" target="_self">Def1</a></i>;<br/>
<b>hence </b><a NAME="E13:22"/>
<font color="Maroon">c<sub>4</sub></font>,<font color="Maroon">c<sub>6</sub></font>,<font color="Maroon">c<sub>5</sub></font>,<font color="Maroon">c<sub>7</sub></font> <a href="projpl_1.html#R5" target="_self">is_a_quadrangle</a> 
 <b>by </b><i><a class="txt" href="projpl_1.html#E7:22"><i><font color="Green">E23</font></i></a>, <a class="txt" href="projpl_1.html#E9:22"><i><font color="Green">E24</font></i></a>, <a class="txt" href="projpl_1.html#E10:22"><i><font color="Green">E25</font></i></a>, <a class="txt" href="projpl_1.html#E11:22"><i><font color="Green">E26</font></i></a>, <a class="ref" href="projpl_1.html#T14" target="_self">Th14</a></i>;<br/>


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