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<b>let </b><font color="Maroon">f</font> be   <a href="funct_1.html#NM1">Function</a>;<br/>

<b>assume </b><a NAME="E1:2"/>
<font color="Maroon">f</font> is <a href="relat_1.html#V2">non-empty</a>
 ;<br/>

<b>hence </b><a NAME="E2:2"/>
not  <a href="xboole_0.html#K1">{}</a>  <a href="hidden.html#R2">in</a>  <a href="relat_1.html#K2">rng</a> <font color="Maroon">f</font>
 <b>by </b><i><a class="ref" href="relat_1.html#D9">RELAT_1:def 9</a></i>; <i><font color="Red">:: according to </font></i><a class="ref" href="setfam_1.html#D9">SETFAM_1:def 9</a><br/>


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