<?xml version="1.0"?>
<div class="add">

<b>let </b><font color="Maroon">c<sub>1</sub></font> be   <a href="midsp_1.html#NM1">MidSp</a>;<br/><b>let </b><font color="Maroon">c<sub>2</sub></font>, <font color="Maroon">c<sub>3</sub></font>, <font color="Maroon">c<sub>4</sub></font> be   <a href="pre_topc.html#NM2">Point</a> of <font color="Maroon">c<sub>1</sub></font>;<br/>







<a NAME="E1:35"/>
( <font color="Maroon">c<sub>2</sub></font> <a href="midsp_1.html#K4">@</a> <font color="Maroon">c<sub>3</sub></font> <a href="hidden.html#R1">=</a> <font color="Maroon">c<sub>4</sub></font> iff <font color="Maroon">c<sub>2</sub></font> <a href="midsp_1.html#K4">@</a> <font color="Maroon">c<sub>3</sub></font> <a href="hidden.html#R1">=</a> <font color="Maroon">c<sub>4</sub></font> <a href="midsp_1.html#K4">@</a> <font color="Maroon">c<sub>4</sub></font> )
 
<b>by </b><i><a class="ref" href="midsp_1.html#D4">MIDSP_1:def 4</a></i>;<br/>
<b>hence </b><a NAME="E2:35"/>
( <font color="Maroon">c<sub>2</sub></font> <a href="midsp_1.html#K4">@</a> <font color="Maroon">c<sub>3</sub></font> <a href="hidden.html#R1">=</a> <font color="Maroon">c<sub>4</sub></font> iff  <a href="midsp_1.html#K12">vect</a> <font color="Maroon">c<sub>2</sub></font>,<font color="Maroon">c<sub>4</sub></font> <a href="hidden.html#R1">=</a>  <a href="midsp_1.html#K12">vect</a> <font color="Maroon">c<sub>4</sub></font>,<font color="Maroon">c<sub>3</sub></font> )
 <b>by </b><i><a class="ref" href="midsp_2.html#T25" target="_self">Th25</a></i>;<br/>


</div>
