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<b>let </b><font color="Maroon">M</font> be    <a href="pboole.html#M1" target="_self">ManySortedSet</a> of <font color="Maroon">I</font>;<br/>

<b>assume </b><a NAME="E1:137_1_1"/><i><font color="Green">E24</font></i>: 
<font color="Maroon">M</font> is <a href="relat_1.html#V2">non-empty</a>
 ;<br/>

<b>consider </b><font color="Maroon">i</font> being    <a href="subset_1.html#M1">Element</a> of <font color="Maroon">I</font>;<br/>
<b>take </b>
<font color="Maroon">i</font>
; <i><font color="Red">:: according to </font></i><a class="ref" href="pboole.html#D15" target="_self">PBOOLE:def 15</a><br/>

<b>thus </b><a NAME="E3:137_1_1"/>
<font color="Maroon">i</font> <a href="hidden.html#R2">in</a> <font color="Maroon">I</font>
 ;<br/>

<b>thus </b><a NAME="E4:137_1_1"/>
not <font color="Maroon">M</font> <a href="funct_1.html#K1">.</a> <font color="Maroon">i</font> is <a href="xboole_0.html#V1">empty</a>
 <b>by </b><i><a class="ref" href="pboole.html#T19" target="_self">Th19</a>, <a class="ref" href="pboole.html#T18" target="_self">Th18</a></i>;<br/>


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