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<b>take </b>
 <a href="pboole.html#K1" target="_self">[0]</a> <font color="Maroon">I</font>
;<br/>

<b>let </b><font color="Maroon">i</font> be    <a href="hidden.html#M1">set</a> ; <i><font color="Red">:: according to </font></i><a class="ref" href="pboole.html#D15" target="_self">PBOOLE:def 15</a><br/>

<b>assume </b><a NAME="E1:136_1_1"/>
<font color="Maroon">i</font> <a href="hidden.html#R2">in</a> <font color="Maroon">I</font>
 ;<br/>

<b>thus </b><a NAME="E2:136_1_1"/>
<span class="p1">(<span class="default"><a href="pboole.html#K1" target="_self">[0]</a> <font color="Maroon">I</font></span>)</span> <a href="funct_1.html#K1">.</a> <font color="Maroon">i</font> is <a href="xboole_0.html#V1">empty</a>
 <b>by </b><i/>;<br/>


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