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<b>let </b><font color="Maroon">X</font> be  non <a href="struct_0.html#V3">empty</a> <a href="pre_topc.html#NM1">TopSpace</a>, <font color="Maroon">Y</font> be  non <a href="struct_0.html#V3">empty</a> <a href="pre_topc.html#NM1">TopSpace</a>;<br/><b>let </b><font color="Maroon">d</font> be   <a href="struct_0.html#NM6">Function</a> of <font color="Maroon">X</font>,<font color="Maroon">Y</font>;<br/>



<a NAME="E1:43"/><i><font color="Green">E44</font></i>: 
(  <a href="waybel18.html#K8">corestr</a> <font color="Maroon">d</font> <a href="hidden.html#R1">=</a> <font color="Maroon">d</font> &amp;  <a href="waybel18.html#K7">Image</a> <font color="Maroon">d</font> <a href="hidden.html#R1">=</a> <font color="Maroon">Y</font> <a href="pre_topc.html#K3">|</a> <span class="p1">(<span class="default"><a href="relset_1.html#K5">rng</a> <font color="Maroon">d</font></span>)</span> )
 
<b>by </b><i><a class="ref" href="waybel18.html#D6">WAYBEL18:def 6</a>, <a class="ref" href="waybel18.html#D7">WAYBEL18:def 7</a></i>;<br/>
<b>thus </b><a NAME="E2:43"/>
( <font color="Maroon">d</font> is <a href="waybel34.html#V2" target="_self">relatively_open</a> implies  <a href="waybel18.html#K8">corestr</a> <font color="Maroon">d</font> is <a href="t_0topsp.html#V1">open</a> )
 <div><a class="txt" onclick="hs2(this)" href="javascript:()" title="43_1"><b>proof </b></a><div class="add">

<b>assume </b><a NAME="E1:43_1"/><i><font color="Green">E45</font></i>: 
for <font color="Olive">V</font> being <a href="pre_topc.html#V3">open</a> <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">X</font> holds  <font color="Maroon">d</font> <a href="relset_1.html#K10">.:</a> <font color="Olive">V</font> is  <a href="pre_topc.html#V3">open</a> <a href="struct_0.html#NM2">Subset</a> of <span class="p1">(<span class="default"><font color="Maroon">Y</font> <a href="pre_topc.html#K3">|</a> <span class="p2">(<span class="default"><a href="relset_1.html#K5">rng</a> <font color="Maroon">d</font></span>)</span></span>)</span>
 ; <i><font color="Red">:: according to </font></i><a class="ref" href="waybel34.html#D9" target="_self">WAYBEL34:def 9</a><br/>

<b>let </b><font color="Maroon">V</font> be   <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">X</font>; <i><font color="Red">:: according to </font></i><a class="ref" href="t_0topsp.html#D2">T_0TOPSP:def 2</a><br/>

<b>assume </b><a NAME="E2:43_1"/>
<font color="Maroon">V</font> is <a href="pre_topc.html#V3">open</a>
 ;<br/>

<b>hence </b><a NAME="E3:43_1"/>
<span class="p1">(<span class="default"><a href="waybel18.html#K8">corestr</a> <font color="Maroon">d</font></span>)</span> <a href="relset_1.html#K10">.:</a> <font color="Maroon">V</font> is <a href="pre_topc.html#V3">open</a>
 <b>by </b><i>, </i>;<br/>


</div><b>end;</b></div>

<b>assume </b><a NAME="E3:43"/><i><font color="Green">E46</font></i>: 
for <font color="Olive">V</font> being  <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">X</font>  st <font color="Olive">V</font> is <a href="pre_topc.html#V3">open</a> holds <br/><span class="p1">(<span class="default"><a href="waybel18.html#K8">corestr</a> <font color="Maroon">d</font></span>)</span> <a href="relset_1.html#K10">.:</a> <font color="Olive">V</font> is <a href="pre_topc.html#V3">open</a>
 ; <i><font color="Red">:: according to </font></i><a class="ref" href="t_0topsp.html#D2">T_0TOPSP:def 2</a><br/>

<b>let </b><font color="Maroon">V</font> be  <a href="pre_topc.html#V3">open</a> <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">X</font>; <i><font color="Red">:: according to </font></i><a class="ref" href="waybel34.html#D9" target="_self">WAYBEL34:def 9</a><br/>

<b>thus </b><a NAME="E4:43"/>
<font color="Maroon">d</font> <a href="relset_1.html#K10">.:</a> <font color="Maroon">V</font> is  <a href="pre_topc.html#V3">open</a> <a href="struct_0.html#NM2">Subset</a> of <span class="p1">(<span class="default"><font color="Maroon">Y</font> <a href="pre_topc.html#K3">|</a> <span class="p2">(<span class="default"><a href="relset_1.html#K5">rng</a> <font color="Maroon">d</font></span>)</span></span>)</span>
 <b>by </b><i>, </i>;<br/>


</div>
