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<b>let </b><font color="Maroon">S</font> be   <a href="subset_1.html#NM2">Subset</a> of <font color="Maroon">E</font>, <font color="Maroon">T</font> be   <a href="subset_1.html#NM2">Subset</a> of <font color="Maroon">E</font>;<br/>

<b>assume </b><a NAME="E1:18_1_2"/><i><font color="Green">E20</font></i>: 
<font color="Maroon">S</font> <a href="hidden.html#R1">=</a> <font color="Maroon">E</font> <a href="xboole_0.html#K4">\</a> <font color="Maroon">T</font>
 ;<br/>

<a NAME="E2:18_1_2"/>
<font color="Maroon">T</font> <a href="hidden.html#R2">in</a>  <a href="zfmisc_1.html#K1">bool</a> <font color="Maroon">E</font>
 
<b>by </b><i/>;<br/>
<a NAME="E3:18_1_2"/><b>then </b>
<font color="Maroon">T</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">E</font>
 
<b>by </b><i><a class="ref" href="zfmisc_1.html#D1">ZFMISC_1:def 1</a></i>;<br/>
<b>hence </b><font color="Maroon">T</font> = 
<a href="xboole_0.html#K1">{}</a>  <a href="xboole_0.html#K2">\/</a> <span class="p1">(<span class="default"><font color="Maroon">E</font> <a href="xboole_0.html#K3">/\</a> <font color="Maroon">T</font></span>)</span>
<b>by </b><i><a class="ref" href="xboole_1.html#T28">XBOOLE_1:28</a></i>
<br/>.= 
<span class="p1">(<span class="default"><font color="Maroon">E</font> <a href="xboole_0.html#K4">\</a> <font color="Maroon">E</font></span>)</span> <a href="xboole_0.html#K2">\/</a> <span class="p1">(<span class="default"><font color="Maroon">E</font> <a href="xboole_0.html#K3">/\</a> <font color="Maroon">T</font></span>)</span>
<b>by </b><i><a class="ref" href="xboole_1.html#T37">XBOOLE_1:37</a></i>
<br/>.= 
<font color="Maroon">E</font> <a href="xboole_0.html#K4">\</a> <font color="Maroon">S</font>
<b>by </b><i>, <a class="ref" href="xboole_1.html#T52">XBOOLE_1:52</a></i>
;<br/><br/>


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