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<b>consider </b><font color="Maroon">a</font> being    <a href="hidden.html#M1">set</a> <b> such that </b><br/><a NAME="E2:2_1"/><i><font color="Green">E9</font></i>: 
for <font color="Olive">b</font> being   <a href="hidden.html#M1">set</a>  holds  <font color="Maroon">P<sub>1</sub></font>[<font color="Maroon">a</font>,<font color="Olive">b</font>]
 <b>by </b><i/>;<br/>
<div><a class="txt" onclick="hs2(this)" href="javascript:()" title="2_1_1"><b>now </b></a><div class="add"><b>let </b><font color="Maroon">b</font> be    <a href="hidden.html#M1">set</a> ;<br/><a NAME="E1:2_1_1"/>
<font color="Maroon">P<sub>1</sub></font>[<font color="Maroon">a</font>,<font color="Maroon">b</font>]
 <b>by </b><i/>;<br/><b>hence </b><a NAME="E2:2_1_1"/>
 ex <font color="Olive">a</font> being   <a href="hidden.html#M1">set</a>  st <font color="Maroon">P<sub>1</sub></font>[<font color="Olive">a</font>,<font color="Maroon">b</font>]
 ;<br/></div><b>end;</b></div>
<b>hence </b><a NAME="E4:2_1"/>
for <font color="Olive">b</font> being   <a href="hidden.html#M1">set</a>   ex <font color="Olive">a</font> being   <a href="hidden.html#M1">set</a>  st <font color="Maroon">P<sub>1</sub></font>[<font color="Olive">a</font>,<font color="Olive">b</font>]
 ;<br/>


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