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<b>let </b><font color="Maroon">N</font> be   <a href="net_1.html#NM1">Pnet</a>;<br/><b>let </b><font color="Maroon">x</font> be    <a href="subset_1.html#M1">Element</a> of  <a href="net_1.html#K1" target="_self">Elements</a> <font color="Maroon">N</font>;<br/><b>let </b><font color="Maroon">X</font> be    <a href="hidden.html#M1">set</a> ;<br/>





<b>assume </b><a NAME="E1:32"/><i><font color="Green">E13</font></i>: 
(  <a href="net_1.html#K1" target="_self">Elements</a> <font color="Maroon">N</font> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a>  <a href="xboole_0.html#K1">{}</a>  &amp; <font color="Maroon">X</font> <a href="tarski.html#R1">c=</a>  <a href="net_1.html#K1" target="_self">Elements</a> <font color="Maroon">N</font> &amp; <font color="Maroon">x</font> <a href="hidden.html#R2">in</a> <font color="Maroon">X</font> )
 ;<br/>

<a NAME="E2:32"/><b>then </b>
 <a href="net_1.html#K5" target="_self">exit</a> <font color="Maroon">N</font>,<font color="Maroon">x</font> <a href="tarski.html#R1">c=</a>  <a href="net_1.html#K1" target="_self">Elements</a> <font color="Maroon">N</font>
 
<b>by </b><i><a class="ref" href="net_1.html#D6" target="_self">Def6</a></i>;<br/>
<b>hence </b><a NAME="E3:32"/>
 <a href="net_1.html#K5" target="_self">exit</a> <font color="Maroon">N</font>,<font color="Maroon">x</font> <a href="hidden.html#R2">in</a>  <a href="net_1.html#K10" target="_self">Ext</a> <font color="Maroon">N</font>,<font color="Maroon">X</font>
 <b>by </b><i>, </i>;<br/>


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