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<b>let </b><font color="Maroon">E</font> be  non <a href="xboole_0.html#V1">empty</a>  <a href="hidden.html#M1">set</a> ;<br/><b>let </b><font color="Maroon">e1</font> be   <a href="rpr_1.html#NM1">El_ev</a> of <font color="Maroon">E</font>;<br/><b>let </b><font color="Maroon">e2</font> be   <a href="rpr_1.html#NM1">El_ev</a> of <font color="Maroon">E</font>;<br/>





<a NAME="E1:15"/>
<font color="Maroon">e1</font> <a href="subset_1.html#K9">/\</a> <font color="Maroon">e2</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">e1</font>
 
<b>by </b><i><a class="ref" href="xboole_1.html#T17">XBOOLE_1:17</a></i>;<br/>
<a NAME="E2:15"/><b>then </b>
( <font color="Maroon">e1</font> <a href="subset_1.html#K9">/\</a> <font color="Maroon">e2</font> <a href="hidden.html#R1">=</a>  <a href="xboole_0.html#K1">{}</a>  or <font color="Maroon">e1</font> <a href="subset_1.html#K9">/\</a> <font color="Maroon">e2</font> <a href="hidden.html#R1">=</a> <font color="Maroon">e1</font> )
 
<b>by </b><i/>;<br/>
<a NAME="E3:15"/><b>then </b>
( <font color="Maroon">e1</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">e2</font> or <font color="Maroon">e1</font> <a href="subset_1.html#K9">/\</a> <font color="Maroon">e2</font> <a href="hidden.html#R1">=</a>  <a href="xboole_0.html#K1">{}</a>  )
 
<b>by </b><i><a class="ref" href="xboole_1.html#T17">XBOOLE_1:17</a></i>;<br/>
<b>hence </b><a NAME="E4:15"/>
( <font color="Maroon">e1</font> <a href="hidden.html#R1">=</a> <font color="Maroon">e2</font> or <font color="Maroon">e1</font> <a href="subset_1.html#R1">misses</a> <font color="Maroon">e2</font> )
 <b>by </b><i>, <a class="ref" href="xboole_0.html#D7">XBOOLE_0:def 7</a></i>;<br/>


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