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<b>let </b><font color="Maroon">FdSp</font> be   <a href="parsp_2.html#NM1">FanodesSp</a>;<br/><b>let </b><font color="Maroon">a</font> be   <a href="struct_0.html#NM1">Element</a> of <font color="Maroon">FdSp</font>;<br/><b>let </b><font color="Maroon">b</font> be   <a href="struct_0.html#NM1">Element</a> of <font color="Maroon">FdSp</font>;<br/><b>let </b><font color="Maroon">c</font> be   <a href="struct_0.html#NM1">Element</a> of <font color="Maroon">FdSp</font>;<br/><b>let </b><font color="Maroon">d</font> be   <a href="struct_0.html#NM1">Element</a> of <font color="Maroon">FdSp</font>;<br/>









<b>assume </b><a NAME="E1:51"/><i><font color="Green">E17</font></i>: 
 <a href="parsp_2.html#R2" target="_self">parallelogram</a> <font color="Maroon">a</font>,<font color="Maroon">b</font>,<font color="Maroon">c</font>,<font color="Maroon">d</font>
 ;<br/>

<a NAME="E2:51"/><b>then </b>
not <font color="Maroon">a</font>,<font color="Maroon">b</font>,<font color="Maroon">c</font> <a href="parsp_2.html#R1" target="_self">is_collinear</a> 
 
<b>by </b><i/>;<br/>
<a NAME="E3:51"/><b>then </b>
( not <font color="Maroon">a</font>,<font color="Maroon">b</font> <a href="parsp_1.html#R1">'||'</a> <font color="Maroon">a</font>,<font color="Maroon">c</font> &amp; <font color="Maroon">a</font>,<font color="Maroon">b</font> <a href="parsp_1.html#R1">'||'</a> <font color="Maroon">c</font>,<font color="Maroon">d</font> &amp; <font color="Maroon">a</font>,<font color="Maroon">c</font> <a href="parsp_1.html#R1">'||'</a> <font color="Maroon">b</font>,<font color="Maroon">d</font> )
 
<b>by </b><i>, , </i>;<br/>
<a NAME="E4:51"/><b>then </b>
not <font color="Maroon">b</font>,<font color="Maroon">c</font> <a href="parsp_1.html#R1">'||'</a> <font color="Maroon">a</font>,<font color="Maroon">d</font>
 
<b>by </b><i><a class="ref" href="parsp_2.html#T1" target="_self">Th1</a></i>;<br/>
<b>hence </b><a NAME="E5:51"/>
not <font color="Maroon">a</font>,<font color="Maroon">d</font> <a href="parsp_1.html#R1">'||'</a> <font color="Maroon">b</font>,<font color="Maroon">c</font>
 <b>by </b><i><a class="ref" href="parsp_1.html#T36">PARSP_1:36</a></i>;<br/>


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