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

<b>let </b><font color="Maroon">T</font> be   <a href="pre_topc.html#NM1">TopSpace</a>;<br/><b>let </b><font color="Maroon">F</font> be   <a href="struct_0.html#NM3">Subset-Family</a> of <font color="Maroon">T</font>;<br/>



<b>thus </b><a NAME="E1:21"/>
( <font color="Maroon">F</font> <a href="hidden.html#R1">=</a>  <a href="xboole_0.html#K1">{}</a>  implies  <a href="tdlat_2.html#K1" target="_self">Int</a> <font color="Maroon">F</font> <a href="hidden.html#R1">=</a>  <a href="xboole_0.html#K1">{}</a>  )
 <div><a class="txt" onclick="hs2(this)" href="javascript:()" title="21_1"><b>proof </b></a><div class="add">

<b>assume </b><a NAME="E1:21_1"/><i><font color="Green">E18</font></i>: 
<font color="Maroon">F</font> <a href="hidden.html#R1">=</a>  <a href="xboole_0.html#K1">{}</a> 
 ;<br/>

<b>consider </b><font color="Maroon">A</font> being    <a href="subset_1.html#M1">Element</a> of  <a href="tdlat_2.html#K1" target="_self">Int</a> <font color="Maroon">F</font>;<br/>
<b>assume </b><a NAME="E3:21_1"/><i><font color="Green">E19</font></i>: 
not  <a href="tdlat_2.html#K1" target="_self">Int</a> <font color="Maroon">F</font> <a href="hidden.html#R1">=</a>  <a href="xboole_0.html#K1">{}</a> 
 ;<br/>

<b>then reconsider </b><font color="Maroon">A</font> = <font color="Maroon">A</font> as   <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">T</font> <b>by </b><i><a class="ref" href="tarski.html#D3">TARSKI:def 3</a></i>;<br/>
<a NAME="E5:21_1"/>
 ex <font color="Olive">V</font> being  <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">T</font> st <br/>( <font color="Maroon">A</font> <a href="hidden.html#R1">=</a>  <a href="tops_1.html#K1">Int</a> <font color="Olive">V</font> &amp; <font color="Olive">V</font> <a href="hidden.html#R2">in</a> <font color="Maroon">F</font> )
 
<b>by </b><i><a class="ref" href="tdlat_2.html#T2" target="_self">Th2</a>, </i>;<br/>
<b>hence </b><a NAME="E6:21_1"/>
contradiction
 <b>by </b><i/>;<br/>


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

<b>thus </b><a NAME="E2:21"/>
(  <a href="tdlat_2.html#K1" target="_self">Int</a> <font color="Maroon">F</font> <a href="hidden.html#R1">=</a>  <a href="xboole_0.html#K1">{}</a>  implies <font color="Maroon">F</font> <a href="hidden.html#R1">=</a>  <a href="xboole_0.html#K1">{}</a>  )
 <div><a class="txt" onclick="hs2(this)" href="javascript:()" title="21_2"><b>proof </b></a><div class="add">

<b>assume </b><a NAME="E1:21_2"/><i><font color="Green">E22</font></i>: 
 <a href="tdlat_2.html#K1" target="_self">Int</a> <font color="Maroon">F</font> <a href="hidden.html#R1">=</a>  <a href="xboole_0.html#K1">{}</a> 
 ;<br/>

<b>consider </b><font color="Maroon">B</font> being    <a href="subset_1.html#M1">Element</a> of <font color="Maroon">F</font>;<br/>
<b>assume </b><a NAME="E3:21_2"/><i><font color="Green">E23</font></i>: 
not <font color="Maroon">F</font> <a href="hidden.html#R1">=</a>  <a href="xboole_0.html#K1">{}</a> 
 ;<br/>

<b>then reconsider </b><font color="Maroon">B</font> = <font color="Maroon">B</font> as   <a href="struct_0.html#NM2">Subset</a> of <font color="Maroon">T</font> <b>by </b><i><a class="ref" href="tarski.html#D3">TARSKI:def 3</a></i>;<br/>
<b>reconsider </b><font color="Maroon">A</font> =  <a href="tops_1.html#K1">Int</a> <font color="Maroon">B</font> as    <a href="hidden.html#M1">set</a>  ;<br/>
<a NAME="E6:21_2"/>
 ex <font color="Olive">A</font> being   <a href="hidden.html#M1">set</a>  st <font color="Olive">A</font> <a href="hidden.html#R2">in</a>  <a href="tdlat_2.html#K1" target="_self">Int</a> <font color="Maroon">F</font>
 
<div><a class="txt" onclick="hs2(this)" href="javascript:()" title="21_2_1"><b>proof </b></a><div class="add">

<b>take </b>
<font color="Maroon">A</font>
;<br/>

<b>thus </b><a NAME="E1:21_2_1"/>
<font color="Maroon">A</font> <a href="hidden.html#R2">in</a>  <a href="tdlat_2.html#K1" target="_self">Int</a> <font color="Maroon">F</font>
 <b>by </b><i><a class="ref" href="tdlat_2.html#T2" target="_self">Th2</a>, </i>;<br/>


</div><b>end;</b></div>
<b>hence </b><a NAME="E7:21_2"/>
contradiction
 <b>by </b><i/>;<br/>


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


</div>
