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<b>let </b><font color="Maroon">c<sub>1</sub></font> be   <a href="classes2.html#NM1">Universe</a>;<br/>

<b>reconsider </b><font color="Maroon">c<sub>2</sub></font> =  <a href="xboole_0.html#K1">{}</a>  as    <a href="subset_1.html#M1">Element</a> of <font color="Maroon">c<sub>1</sub></font> <b>by </b><i><a class="ref" href="classes2.html#T62">CLASSES2:62</a></i>;<br/>
<b>set </b><font color="Maroon">c<sub>3</sub></font> = <span class="p1"><a href="classes2.html#K1">{</a><span class="default"><font color="Maroon">c<sub>2</sub></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">c<sub>2</sub></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">c<sub>4</sub></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">c<sub>1</sub></font> ;<br/>
<b>reconsider </b><font color="Maroon">c<sub>5</sub></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">c<sub>1</sub></font> <b>by </b><i><a class="ref" href="grcat_1.html#T6" target="_self">Th6</a>, <a class="ref" href="grcat_1.html#T13" target="_self">Th13</a></i>;<br/>
<b>reconsider </b><font color="Maroon">c<sub>6</sub></font> =  <a href="midsp_1.html#K2">op2</a>  as    <a href="subset_1.html#M1">Element</a> of <font color="Maroon">c<sub>1</sub></font> <b>by </b><i><a class="ref" href="grcat_1.html#T6" target="_self">Th6</a></i>;<br/>
<b>set </b><font color="Maroon">c<sub>7</sub></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">c<sub>2</sub></font></span><a href="classes2.html#K1">}</a></span>,<font color="Maroon">c<sub>6</sub></font>,<font color="Maroon">c<sub>5</sub></font>,<font color="Maroon">c<sub>4</sub></font></span><a href="domain_1.html#K5">]</a></span>;<br/>
<a NAME="E6:79"/><i><font color="Green">E43</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">c<sub>2</sub></font></span><a href="classes2.html#K1">}</a></span>,<font color="Maroon">c<sub>6</sub></font>,<font color="Maroon">c<sub>5</sub></font>,<font color="Maroon">c<sub>4</sub></font></span><a href="domain_1.html#K5">]</a></span> is    <a href="subset_1.html#M1">Element</a> of <font color="Maroon">c<sub>1</sub></font>
 
<b>by </b><i><a class="ref" href="grcat_1.html#T3" target="_self">Th3</a></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">c<sub>2</sub></font></span><a href="classes2.html#K1">}</a></span>,<font color="Maroon">c<sub>6</sub></font>,<font color="Maroon">c<sub>5</sub></font>,<font color="Maroon">c<sub>4</sub></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">c<sub>2</sub></font></span><a href="classes2.html#K1">}</a></span>,<font color="Maroon">c<sub>6</sub></font>,<font color="Maroon">c<sub>5</sub></font>,<font color="Maroon">c<sub>4</sub></font></span><a href="domain_1.html#K5">]</a></span> <a href="hidden.html#R2">in</a> <font color="Maroon">c<sub>1</sub></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">c<sub>2</sub></font></span><a href="classes2.html#K1">}</a></span>,<font color="Maroon">c<sub>6</sub></font>,<font color="Maroon">c<sub>5</sub></font>,<font color="Maroon">c<sub>4</sub></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="txt" href="grcat_1.html#E6:79"><i><font color="Green">E43</font></i></a>, <a class="ref" href="grcat_1.html#D28" target="_self">Def28</a>, <a class="ref" href="algstr_1.html#D4">ALGSTR_1:def 4</a></i>;<br/>


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