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<b>let </b><font color="Maroon" title="c1">AS</font> be   <a href="dirort.html#NM1" title="DIRORT:NM.1">Oriented_Orthogonality_Space</a>;<br/><b>let </b><font color="Maroon" title="c2">u</font>, <font color="Maroon" title="c3">u1</font>, <font color="Maroon" title="c4">v</font>, <font color="Maroon" title="c5">v1</font> be   <a href="struct_0.html#NM1" title="STRUCT_0:NM.1">Element</a> of <font color="Maroon" title="c1">AS</font>;<br/>









<b>assume </b><a NAME="E1:19"/>
<font color="Maroon" title="c2">u</font>,<font color="Maroon" title="c3">u1</font> <a href="dirort.html#R2" title="DIRORT:pred.2">//</a> <font color="Maroon" title="c4">v</font>,<font color="Maroon" title="c5">v1</font>
 ;<br/>

<a NAME="E2:19"/><b>then </b>
 ex <font color="Olive" title="b1">w</font>, <font color="Olive" title="b2">w1</font> being  <a href="struct_0.html#NM1" title="STRUCT_0:NM.1">Element</a> of <font color="Maroon" title="c1">AS</font> st <br/>( <font color="Olive" title="b1">w</font> <a href="hidden.html#NR2" title="HIDDEN:NR.2">&lt;&gt;</a> <font color="Olive" title="b2">w1</font> &amp; <font color="Olive" title="b1">w</font>,<font color="Olive" title="b2">w1</font> <a href="dirort.html#NR1" title="DIRORT:NR.1">'//'</a> <font color="Maroon" title="c2">u</font>,<font color="Maroon" title="c3">u1</font> &amp; <font color="Olive" title="b1">w</font>,<font color="Olive" title="b2">w1</font> <a href="dirort.html#NR1" title="DIRORT:NR.1">'//'</a> <font color="Maroon" title="c4">v</font>,<font color="Maroon" title="c5">v1</font> )
 
<b>by </b><i><a class="ref" href="dirort.html#D3" target="_self" title="DIRORT:def.3">Def3</a></i>;<br/>
<b>hence </b><a NAME="E3:19"/>
<font color="Maroon" title="c4">v</font>,<font color="Maroon" title="c5">v1</font> <a href="dirort.html#R2" title="DIRORT:pred.2">//</a> <font color="Maroon" title="c2">u</font>,<font color="Maroon" title="c3">u1</font>
 <b>by </b><i><a class="ref" href="dirort.html#D3" target="_self" title="DIRORT:def.3">Def3</a></i>;<br/>


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