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<b>let </b><font color="Maroon">FT</font> be  non <a href="struct_0.html#V3">empty</a>  <a href="orders_2.html#L1">RelStr</a> ;<br/><b>let </b><font color="Maroon">x</font> be   <a href="struct_0.html#NM1">Element</a> of <font color="Maroon">FT</font>;<br/><b>let </b><font color="Maroon">A</font> be   <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">FT</font>;<br/>





<a NAME="E1:14"/><i><font color="Green">E19</font></i>: 
( <font color="Maroon">x</font> <a href="hidden.html#R2">in</a> <font color="Maroon">A</font> <a href="fin_topo.html#K7">^deltao</a>  implies (  ex <font color="Olive">y1</font>, <font color="Olive">y2</font> being  <a href="struct_0.html#NM1">Element</a> of <font color="Maroon">FT</font> st <br/>(  <a href="fintopo2.html#K1" target="_self">P_1</a> <font color="Maroon">x</font>,<font color="Olive">y1</font>,<font color="Maroon">A</font> <a href="hidden.html#R1">=</a>  <a href="margrel1.html#K8">TRUE</a>  &amp;  <a href="fintopo2.html#K2" target="_self">P_2</a> <font color="Maroon">x</font>,<font color="Olive">y2</font>,<font color="Maroon">A</font> <a href="hidden.html#R1">=</a>  <a href="margrel1.html#K8">TRUE</a>  ) &amp;  <a href="fintopo2.html#K4" target="_self">P_A</a> <font color="Maroon">x</font>,<font color="Maroon">A</font> <a href="hidden.html#R1">=</a>  <a href="margrel1.html#K7">FALSE</a>  ) )
 
<div><a class="txt" onclick="hs2(this)" href="javascript:()" title="14_1"><b>proof </b></a><div class="add">

<b>assume </b><a NAME="E1:14_1"/>
<font color="Maroon">x</font> <a href="hidden.html#R2">in</a> <font color="Maroon">A</font> <a href="fin_topo.html#K7">^deltao</a> 
 ;<br/>

<a NAME="E2:14_1"/><b>then </b>
<font color="Maroon">x</font> <a href="hidden.html#R2">in</a> <span class="p1">(<span class="default"><font color="Maroon">A</font> <a href="subset_1.html#K3">`</a> </span>)</span> <a href="subset_1.html#K9">/\</a> <span class="p1">(<span class="default"><font color="Maroon">A</font> <a href="fin_topo.html#K5">^delta</a> </span>)</span>
 
<b>by </b><i><a class="ref" href="fin_topo.html#D9">FIN_TOPO:def 9</a></i>;<br/>
<a NAME="E3:14_1"/><b>then </b>
( <font color="Maroon">x</font> <a href="hidden.html#R2">in</a> <font color="Maroon">A</font> <a href="subset_1.html#K3">`</a>  &amp; <font color="Maroon">x</font> <a href="hidden.html#R2">in</a> <font color="Maroon">A</font> <a href="fin_topo.html#K5">^delta</a>  )
 
<b>by </b><i><a class="ref" href="xboole_0.html#D3">XBOOLE_0:def 3</a></i>;<br/>
<a NAME="E4:14_1"/><b>then </b>
( not <font color="Maroon">x</font> <a href="hidden.html#R2">in</a> <font color="Maroon">A</font> &amp; <font color="Maroon">x</font> <a href="hidden.html#R2">in</a> <font color="Maroon">A</font> <a href="fin_topo.html#K5">^delta</a>  )
 
<b>by </b><i><a class="ref" href="xboole_0.html#D4">XBOOLE_0:def 4</a></i>;<br/>
<b>hence </b><a NAME="E5:14_1"/>
(  ex <font color="Olive">y1</font>, <font color="Olive">y2</font> being  <a href="struct_0.html#NM1">Element</a> of <font color="Maroon">FT</font> st <br/>(  <a href="fintopo2.html#K1" target="_self">P_1</a> <font color="Maroon">x</font>,<font color="Olive">y1</font>,<font color="Maroon">A</font> <a href="hidden.html#R1">=</a>  <a href="margrel1.html#K8">TRUE</a>  &amp;  <a href="fintopo2.html#K2" target="_self">P_2</a> <font color="Maroon">x</font>,<font color="Olive">y2</font>,<font color="Maroon">A</font> <a href="hidden.html#R1">=</a>  <a href="margrel1.html#K8">TRUE</a>  ) &amp;  <a href="fintopo2.html#K4" target="_self">P_A</a> <font color="Maroon">x</font>,<font color="Maroon">A</font> <a href="hidden.html#R1">=</a>  <a href="margrel1.html#K7">FALSE</a>  )
 <b>by </b><i>, </i>;<br/>


</div><b>end;</b></div>
<a NAME="E2:14"/>
(  ex <font color="Olive">y1</font>, <font color="Olive">y2</font> being  <a href="struct_0.html#NM1">Element</a> of <font color="Maroon">FT</font> st <br/>(  <a href="fintopo2.html#K1" target="_self">P_1</a> <font color="Maroon">x</font>,<font color="Olive">y1</font>,<font color="Maroon">A</font> <a href="hidden.html#R1">=</a>  <a href="margrel1.html#K8">TRUE</a>  &amp;  <a href="fintopo2.html#K2" target="_self">P_2</a> <font color="Maroon">x</font>,<font color="Olive">y2</font>,<font color="Maroon">A</font> <a href="hidden.html#R1">=</a>  <a href="margrel1.html#K8">TRUE</a>  ) &amp;  <a href="fintopo2.html#K4" target="_self">P_A</a> <font color="Maroon">x</font>,<font color="Maroon">A</font> <a href="hidden.html#R1">=</a>  <a href="margrel1.html#K7">FALSE</a>  implies <font color="Maroon">x</font> <a href="hidden.html#R2">in</a> <font color="Maroon">A</font> <a href="fin_topo.html#K7">^deltao</a>  )
 
<div><a class="txt" onclick="hs2(this)" href="javascript:()" title="14_2"><b>proof </b></a><div class="add">

<b>assume </b><a NAME="E1:14_2"/>
(  ex <font color="Olive">y1</font>, <font color="Olive">y2</font> being  <a href="struct_0.html#NM1">Element</a> of <font color="Maroon">FT</font> st <br/>(  <a href="fintopo2.html#K1" target="_self">P_1</a> <font color="Maroon">x</font>,<font color="Olive">y1</font>,<font color="Maroon">A</font> <a href="hidden.html#R1">=</a>  <a href="margrel1.html#K8">TRUE</a>  &amp;  <a href="fintopo2.html#K2" target="_self">P_2</a> <font color="Maroon">x</font>,<font color="Olive">y2</font>,<font color="Maroon">A</font> <a href="hidden.html#R1">=</a>  <a href="margrel1.html#K8">TRUE</a>  ) &amp;  <a href="fintopo2.html#K4" target="_self">P_A</a> <font color="Maroon">x</font>,<font color="Maroon">A</font> <a href="hidden.html#R1">=</a>  <a href="margrel1.html#K7">FALSE</a>  )
 ;<br/>

<a NAME="E2:14_2"/><b>then </b>
( <font color="Maroon">x</font> <a href="hidden.html#R2">in</a> <font color="Maroon">A</font> <a href="fin_topo.html#K5">^delta</a>  &amp; <font color="Maroon">x</font> <a href="hidden.html#R2">in</a> the <a href="struct_0.html#U1">carrier</a> of <font color="Maroon">FT</font> &amp; not <font color="Maroon">x</font> <a href="hidden.html#R2">in</a> <font color="Maroon">A</font> )
 
<b>by </b><i>, </i>;<br/>
<a NAME="E3:14_2"/><b>then </b>
( <font color="Maroon">x</font> <a href="hidden.html#R2">in</a> <font color="Maroon">A</font> <a href="fin_topo.html#K5">^delta</a>  &amp; <font color="Maroon">x</font> <a href="hidden.html#R2">in</a> the <a href="struct_0.html#U1">carrier</a> of <font color="Maroon">FT</font> <a href="subset_1.html#K6">\</a> <font color="Maroon">A</font> )
 
<b>by </b><i><a class="ref" href="xboole_0.html#D4">XBOOLE_0:def 4</a></i>;<br/>
<a NAME="E4:14_2"/><b>then </b>
( <font color="Maroon">x</font> <a href="hidden.html#R2">in</a> <font color="Maroon">A</font> <a href="fin_topo.html#K5">^delta</a>  &amp; <font color="Maroon">x</font> <a href="hidden.html#R2">in</a> <font color="Maroon">A</font> <a href="subset_1.html#K3">`</a>  )
 
;<br/>
<a NAME="E5:14_2"/><b>then </b>
<font color="Maroon">x</font> <a href="hidden.html#R2">in</a> <span class="p1">(<span class="default"><font color="Maroon">A</font> <a href="subset_1.html#K3">`</a> </span>)</span> <a href="subset_1.html#K9">/\</a> <span class="p1">(<span class="default"><font color="Maroon">A</font> <a href="fin_topo.html#K5">^delta</a> </span>)</span>
 
<b>by </b><i><a class="ref" href="xboole_0.html#D3">XBOOLE_0:def 3</a></i>;<br/>
<b>hence </b><a NAME="E6:14_2"/>
<font color="Maroon">x</font> <a href="hidden.html#R2">in</a> <font color="Maroon">A</font> <a href="fin_topo.html#K7">^deltao</a> 
 <b>by </b><i><a class="ref" href="fin_topo.html#D9">FIN_TOPO:def 9</a></i>;<br/>


</div><b>end;</b></div>
<b>hence </b><a NAME="E3:14"/>
( <font color="Maroon">x</font> <a href="hidden.html#R2">in</a> <font color="Maroon">A</font> <a href="fin_topo.html#K7">^deltao</a>  iff (  ex <font color="Olive">y1</font>, <font color="Olive">y2</font> being  <a href="struct_0.html#NM1">Element</a> of <font color="Maroon">FT</font> st <br/>(  <a href="fintopo2.html#K1" target="_self">P_1</a> <font color="Maroon">x</font>,<font color="Olive">y1</font>,<font color="Maroon">A</font> <a href="hidden.html#R1">=</a>  <a href="margrel1.html#K8">TRUE</a>  &amp;  <a href="fintopo2.html#K2" target="_self">P_2</a> <font color="Maroon">x</font>,<font color="Olive">y2</font>,<font color="Maroon">A</font> <a href="hidden.html#R1">=</a>  <a href="margrel1.html#K8">TRUE</a>  ) &amp;  <a href="fintopo2.html#K4" target="_self">P_A</a> <font color="Maroon">x</font>,<font color="Maroon">A</font> <a href="hidden.html#R1">=</a>  <a href="margrel1.html#K7">FALSE</a>  ) )
 <b>by </b><i/>;<br/>


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