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<a NAME="E1:43_1_1"/>
 <a href="xboole_0.html#K1">{}</a>  is   <a href="funct_1.html#NM1">Function</a>
 
;<br/>
<b>hence </b><a NAME="E2:43_1_1"/>
ex <font color="Olive">b<sub>1</sub></font> being  <a href="funct_1.html#NM1">Function</a> st <font color="Olive">b<sub>1</sub></font> is <a href="xboole_0.html#V1">empty</a>
 ;<br/>


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