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<b>let </b><font color="Maroon">UN</font> be   <a href="classes2.html#NM1">Universe</a>;<br/>

<b>reconsider </b><font color="Maroon">u</font> =  <a href="xboole_0.html#K1">{}</a>  as    <a href="subset_1.html#M1">Element</a> of <font color="Maroon">UN</font> <b>by </b><i><a class="ref" href="classes2.html#T62">CLASSES2:62</a></i>;<br/>
<b>set </b><font color="Maroon">x1</font> = <span class="p1"><a href="classes2.html#K1">{</a><span class="default"><font color="Maroon">u</font></span><a href="classes2.html#K1">}</a></span>;<br/>
<a NAME="E2:79"/>
 <a href="algstr_1.html#K1">Extract</a> <a href="xboole_0.html#K1">{}</a>  <a href="hidden.html#R1">=</a> <font color="Maroon">u</font>
 
<b>by </b><i><a class="ref" href="algstr_1.html#D3">ALGSTR_1:def 3</a></i>;<br/>
<b>then reconsider </b><font color="Maroon">x4</font> =  <a href="algstr_1.html#K1">Extract</a> <a href="xboole_0.html#K1">{}</a>  as    <a href="subset_1.html#M1">Element</a> of <font color="Maroon">UN</font> ;<br/>
<b>reconsider </b><font color="Maroon">x3</font> =  <a href="vectsp_1.html#K7">comp</a> <a href="algstr_1.html#K2">L_Trivial</a>  as    <a href="subset_1.html#M1">Element</a> of <font color="Maroon">UN</font> <b>by </b><i>, </i>;<br/>
<b>reconsider </b><font color="Maroon">x2</font> =  <a href="midsp_1.html#K2">op2</a>  as    <a href="subset_1.html#M1">Element</a> of <font color="Maroon">UN</font> <b>by </b><i/>;<br/>
<b>set </b><font color="Maroon">x</font> = <span class="p1"><a href="domain_1.html#K5">[</a><span class="default"><span class="p2"><a href="classes2.html#K1">{</a><span class="default"><font color="Maroon">u</font></span><a href="classes2.html#K1">}</a></span>,<font color="Maroon">x2</font>,<font color="Maroon">x3</font>,<font color="Maroon">x4</font></span><a href="domain_1.html#K5">]</a></span>;<br/>
<a NAME="E6:79"/><i><font color="Green">E29</font></i>: 
<span class="p1"><a href="domain_1.html#K5">[</a><span class="default"><span class="p2"><a href="classes2.html#K1">{</a><span class="default"><font color="Maroon">u</font></span><a href="classes2.html#K1">}</a></span>,<font color="Maroon">x2</font>,<font color="Maroon">x3</font>,<font color="Maroon">x4</font></span><a href="domain_1.html#K5">]</a></span> is    <a href="subset_1.html#M1">Element</a> of <font color="Maroon">UN</font>
 
<b>by </b><i/>;<br/>
<b>take </b>
<span class="p1"><a href="domain_1.html#K5">[</a><span class="default"><span class="p2"><a href="classes2.html#K1">{</a><span class="default"><font color="Maroon">u</font></span><a href="classes2.html#K1">}</a></span>,<font color="Maroon">x2</font>,<font color="Maroon">x3</font>,<font color="Maroon">x4</font></span><a href="domain_1.html#K5">]</a></span>
;<br/>

<b>thus </b><a NAME="E7:79"/>
( <span class="p1"><a href="domain_1.html#K5">[</a><span class="default"><span class="p2"><a href="classes2.html#K1">{</a><span class="default"><font color="Maroon">u</font></span><a href="classes2.html#K1">}</a></span>,<font color="Maroon">x2</font>,<font color="Maroon">x3</font>,<font color="Maroon">x4</font></span><a href="domain_1.html#K5">]</a></span> <a href="hidden.html#R2">in</a> <font color="Maroon">UN</font> &amp;  <a href="grcat_1.html#R1" target="_self">GO</a> <span class="p1"><a href="domain_1.html#K5">[</a><span class="default"><span class="p2"><a href="classes2.html#K1">{</a><span class="default"><font color="Maroon">u</font></span><a href="classes2.html#K1">}</a></span>,<font color="Maroon">x2</font>,<font color="Maroon">x3</font>,<font color="Maroon">x4</font></span><a href="domain_1.html#K5">]</a></span>, <a href="algstr_1.html#K2">L_Trivial</a>  )
 <b>by </b><i>, , <a class="ref" href="algstr_1.html#D4">ALGSTR_1:def 4</a></i>;<br/>


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