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<b>let </b><font color="Maroon">c<sub>1</sub></font> be    <a href="hidden.html#M1">set</a> ;<br/><b>let </b><font color="Maroon">c<sub>2</sub></font>, <font color="Maroon">c<sub>3</sub></font> be    <a href="pboole.html#M1" target="_self">ManySortedSet</a> of <font color="Maroon">c<sub>1</sub></font>;<br/>





<b>assume </b><a NAME="E1:142"/><i><font color="Green">E76</font></i>: 
<font color="Maroon">c<sub>2</sub></font> is <a href="relat_1.html#V2">non-empty</a>
 ;<br/>

<b>assume </b><a NAME="E2:142"/>
<font color="Maroon">c<sub>2</sub></font> <a href="pboole.html#R7" target="_self">[=</a> <font color="Maroon">c<sub>3</sub></font>
 ;<br/>

<a NAME="E3:142"/><b>then </b>
<font color="Maroon">c<sub>2</sub></font> <a href="pboole.html#R2" target="_self">c=</a> <font color="Maroon">c<sub>3</sub></font>
 
<b>by </b><i><a class="txt" href="pboole.html#E1:142"><i><font color="Green">E76</font></i></a>, <a class="ref" href="pboole.html#T144" target="_self">Th144</a></i>;<br/>
<b>hence </b><a NAME="E4:142"/>
<font color="Maroon">c<sub>3</sub></font> is <a href="relat_1.html#V2">non-empty</a>
 <b>by </b><i><a class="txt" href="pboole.html#E1:142"><i><font color="Green">E76</font></i></a>, <a class="ref" href="pboole.html#T143" target="_self">Th143</a></i>;<br/>


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