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<b>let </b><font color="Maroon">AS</font> be   <a href="dirort.html#NM1">Oriented_Orthogonality_Space</a>;<br/><b>let </b><font color="Maroon">u</font> be   <a href="struct_0.html#NM1">Element</a> of <font color="Maroon">AS</font>;<br/><b>let </b><font color="Maroon">u1</font> be   <a href="struct_0.html#NM1">Element</a> of <font color="Maroon">AS</font>;<br/><b>let </b><font color="Maroon">v</font> be   <a href="struct_0.html#NM1">Element</a> of <font color="Maroon">AS</font>;<br/><b>let </b><font color="Maroon">v1</font> be   <a href="struct_0.html#NM1">Element</a> of <font color="Maroon">AS</font>;<br/>









<b>assume </b><a NAME="E1:20"/>
<font color="Maroon">u</font>,<font color="Maroon">u1</font> <a href="dirort.html#R2" target="_self">//</a> <font color="Maroon">v</font>,<font color="Maroon">v1</font>
 ;<br/>

<b>then consider </b><font color="Maroon">w</font> being   <a href="struct_0.html#NM1">Element</a> of <font color="Maroon">AS</font>, <font color="Maroon">w1</font> being   <a href="struct_0.html#NM1">Element</a> of <font color="Maroon">AS</font><b> such that </b><br/><a NAME="E3:20"/><i><font color="Green">E20</font></i>: 
( <font color="Maroon">w</font> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a> <font color="Maroon">w1</font> &amp; <font color="Maroon">w</font>,<font color="Maroon">w1</font> <a href="dirort.html#NR1" target="_self">'//'</a> <font color="Maroon">u</font>,<font color="Maroon">u1</font> &amp; <font color="Maroon">w</font>,<font color="Maroon">w1</font> <a href="dirort.html#NR1" target="_self">'//'</a> <font color="Maroon">v</font>,<font color="Maroon">v1</font> )
 <b>by </b><i/>;<br/>
<a NAME="E4:20"/>
( <font color="Maroon">w1</font> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a> <font color="Maroon">w</font> &amp; <font color="Maroon">w1</font>,<font color="Maroon">w</font> <a href="dirort.html#NR1" target="_self">'//'</a> <font color="Maroon">u1</font>,<font color="Maroon">u</font> &amp; <font color="Maroon">w1</font>,<font color="Maroon">w</font> <a href="dirort.html#NR1" target="_self">'//'</a> <font color="Maroon">v1</font>,<font color="Maroon">v</font> )
 
<b>by </b><i>, </i>;<br/>
<b>hence </b><a NAME="E5:20"/>
<font color="Maroon">u1</font>,<font color="Maroon">u</font> <a href="dirort.html#R2" target="_self">//</a> <font color="Maroon">v1</font>,<font color="Maroon">v</font>
 <b>by </b><i/>;<br/>


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