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<a NAME="E1:135_2_1"/>
 <a href="relat_1.html#K1">dom</a> <font color="Maroon">X</font> <a href="hidden.html#R1">=</a> <font color="Maroon">I</font>
 
<b>by </b><i/>;<br/>
<b>hence </b><a NAME="E2:135_2_1"/>
( <font color="Maroon">X</font> is <a href="relat_1.html#V2">non-empty</a> iff for <font color="Olive">i</font> being   <a href="hidden.html#M1">set</a>   st <font color="Olive">i</font> <a href="hidden.html#R2">in</a> <font color="Maroon">I</font> holds <br/> not <font color="Maroon">X</font> <a href="funct_1.html#K1">.</a> <font color="Olive">i</font> is <a href="xboole_0.html#V1">empty</a> )
 <b>by </b><i><a class="ref" href="funct_1.html#D15">FUNCT_1:def 15</a></i>;<br/>


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