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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>assume </b><a NAME="E1:61_1_1"/>
not <font color="Maroon">c<sub>1</sub></font> is <a href="setfam_1.html#V2" target="_self">empty-membered</a>
 ;<br/>

<a NAME="E2:61_1_1"/><b>then </b>
ex <font color="Olive">b<sub>1</sub></font> being non <a href="xboole_0.html#V1">empty</a>  <a href="hidden.html#M1">set</a>  st <font color="Olive">b<sub>1</sub></font> <a href="hidden.html#R2">in</a> <font color="Maroon">c<sub>1</sub></font>
 
<b>by </b><i><a class="ref" href="setfam_1.html#D11" target="_self">Def11</a></i>;<br/>
<b>hence </b><a NAME="E3:61_1_1"/>
not <font color="Maroon">c<sub>1</sub></font> is <a href="xboole_0.html#V1">empty</a>
 ;<br/>


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