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<a NAME="E1:18_3_1"/><i><font color="Green">E21</font></i>: 
( <font color="Maroon">A</font> <a href="hidden.html#R2">in</a>  <a href="zfmisc_1.html#K1">bool</a> <font color="Maroon">E</font> &amp; <font color="Maroon">B</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="E2:18_3_1"/><i><font color="Green">E35</font></i>: 
( <font color="Maroon">A</font> <a href="xboole_0.html#K4">\</a> <font color="Maroon">B</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">A</font> &amp; <font color="Maroon">B</font> <a href="xboole_0.html#K4">\</a> <font color="Maroon">A</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">B</font> )
 
<b>by </b><i><a class="ref" href="xboole_1.html#T36">XBOOLE_1:36</a></i>;<br/>
<a NAME="E3:18_3_1"/>
( <font color="Maroon">A</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">E</font> &amp; <font color="Maroon">B</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/>
<a NAME="E4:18_3_1"/><b>then </b>
( <font color="Maroon">A</font> <a href="xboole_0.html#K4">\</a> <font color="Maroon">B</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">E</font> &amp; <font color="Maroon">B</font> <a href="xboole_0.html#K4">\</a> <font color="Maroon">A</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">E</font> )
 
<b>by </b><i>, <a class="ref" href="xboole_1.html#T1">XBOOLE_1:1</a></i>;<br/>
<a NAME="E5:18_3_1"/><b>then </b>
<span class="p1">(<span class="default"><font color="Maroon">A</font> <a href="xboole_0.html#K4">\</a> <font color="Maroon">B</font></span>)</span> <a href="xboole_0.html#K2">\/</a> <span class="p1">(<span class="default"><font color="Maroon">B</font> <a href="xboole_0.html#K4">\</a> <font color="Maroon">A</font></span>)</span> <a href="tarski.html#R1">c=</a> <font color="Maroon">E</font>
 
<b>by </b><i><a class="ref" href="xboole_1.html#T8">XBOOLE_1:8</a></i>;<br/>
<a NAME="E6:18_3_1"/><b>then </b>
<font color="Maroon">A</font> <a href="xboole_0.html#K5">\+\</a> <font color="Maroon">B</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><a class="ref" href="zfmisc_1.html#D1">ZFMISC_1:def 1</a></i>;<br/>
<b>hence </b><a NAME="E7:18_3_1"/>
<font color="Maroon">A</font> <a href="xboole_0.html#K5">\+\</a> <font color="Maroon">B</font> is   <a href="subset_1.html#NM2">Subset</a> of <font color="Maroon">E</font>
 <b>by </b><i/>;<br/>


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