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<b>let </b><font color="Maroon" title="c4">S</font> be   <a href="struct_0.html#NM2" title="STRUCT_0:NM.2">Subset</a> of <font color="Maroon" title="c3">P</font>;<br/>

<b>assume </b><a NAME="E1:196_1_1"/><i><font color="Green" title="E65">a1</font></i>: 
<font color="Maroon" title="c4">S</font> is <a href="xboole_0.html#V1" title="XBOOLE_0:attr.1">empty</a>
 ;<br/>

<b>let </b><font color="Maroon" title="c5">x</font> be   <a href="struct_0.html#NM1" title="STRUCT_0:NM.1">Element</a> of <font color="Maroon" title="c3">P</font>; <i><font color="Red">:: according to </font></i><a class="ref" href="pcs_0.html#D43" target="_self" title="PCS_0:def.43">PCS_0:def 43</a><br/>

<b>thus </b><a NAME="E2:196_1_1"/>
for <font color="Olive" title="b1">y</font> being  <a href="struct_0.html#NM1" title="STRUCT_0:NM.1">Element</a> of <font color="Maroon" title="c3">P</font>  st <font color="Maroon" title="c5">x</font> <a href="hidden.html#R2" title="HIDDEN:pred.2">in</a> <font color="Maroon" title="c4">S</font> &amp; <font color="Olive" title="b1">y</font> <a href="hidden.html#R2" title="HIDDEN:pred.2">in</a> <font color="Maroon" title="c4">S</font> holds <br/><font color="Maroon" title="c5">x</font> <a href="pcs_0.html#R1" title="PCS_0:pred.1">(--)</a> <font color="Olive" title="b1">y</font>
 <b>by </b><i><a class="txt" href="pcs_0.html#E1:196_1_1"><i><font color="Green" title="E65">a1</font></i></a></i>;<br/>


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