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<b>let </b><font color="Maroon" title="c1">AS</font> be   <a href="diraf.html#NM1" title="DIRAF:NM.1">AffinSpace</a>;<br/><b>let </b><font color="Maroon" title="c2">X</font>, <font color="Maroon" title="c3">A</font>, <font color="Maroon" title="c4">Y</font> be   <a href="struct_0.html#NM2" title="STRUCT_0:NM.2">Subset</a> of <font color="Maroon" title="c1">AS</font>;<br/>







<b>assume </b><b>that </b><br/><a NAME="E1:6"/><i><font color="Green" title="E6">A1</font></i>: 
<font color="Maroon" title="c2">X</font> <a href="aff_4.html#NR1" title="AFF_4:NR.1">is_plane</a> 
 <b>and </b><br/><a NAME="E2:6"/><i><font color="Green" title="E7">A2</font></i>: 
( <font color="Maroon" title="c3">A</font> <a href="aff_4.html#R1" title="AFF_4:pred.1">'||'</a> <font color="Maroon" title="c2">X</font> &amp; <font color="Maroon" title="c2">X</font> <a href="aff_4.html#R1" title="AFF_4:pred.1">'||'</a> <font color="Maroon" title="c4">Y</font> )
 ;<br/>

<a NAME="E3:6"/>
<font color="Maroon" title="c2">X</font> <a href="hidden.html#NR2" title="HIDDEN:NR.2">&lt;&gt;</a>  <a href="xboole_0.html#K1" title="XBOOLE_0:func.1">{}</a> 
 
<b>by </b><i><a class="txt" href="afproj.html#E1:6"><i><font color="Green" title="E6">A1</font></i></a>, <a class="ref" href="aff_4.html#T59" title="AFF_4:th.59">AFF_4:59</a></i>;<br/>
<b>hence </b><a NAME="E4:6"/>
<font color="Maroon" title="c3">A</font> <a href="aff_4.html#R1" title="AFF_4:pred.1">'||'</a> <font color="Maroon" title="c4">Y</font>
 <b>by </b><i><a class="txt" href="afproj.html#E2:6"><i><font color="Green" title="E7">A2</font></i></a>, <a class="ref" href="aff_4.html#T60" title="AFF_4:th.60">AFF_4:60</a></i>;<br/>


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