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<b>let </b><font color="Maroon">X</font> be    <a href="hidden.html#M1">set</a> ;<br/>

<a NAME="E1:61"/>
( <font color="Maroon">X</font> <a href="hidden.html#R1">=</a>  <a href="xboole_0.html#K1">{}</a>  implies <font color="Maroon">X</font> <a href="hidden.html#R1">=</a>  <a href="xboole_0.html#K1">{}</a>  )
 
;<br/>
<b>hence </b><a NAME="E2:61"/>
for <font color="Olive">f</font> being  <a href="funct_2.html#NM1">Function</a> of <font color="Maroon">X</font>,<font color="Maroon">X</font> holds   <a href="relset_1.html#K4">dom</a> <font color="Olive">f</font> <a href="hidden.html#R1">=</a> <font color="Maroon">X</font>
 <b>by </b><i/>;<br/>


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