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<b>set </b><font color="Maroon">c<sub>4</sub></font> = <span class="p1">{<span class="default"> <span class="p2"><a href="pralg_2.html#K7" target="_self">|.</a><span class="default"><span class="p3">(<span class="default"><font color="Maroon">c<sub>3</sub></font> <a href="pralg_2.html#K6" target="_self">.</a> <font color="Olive">b<sub>1</sub></font></span>)</span></span><a href="pralg_2.html#K7" target="_self">.|</a></span> where B is    <a href="subset_1.html#M1">Element</a> of <font color="Maroon">c<sub>1</sub></font> : verum </span>}</span> ;<br/>
<b>consider </b><font color="Maroon">c<sub>5</sub></font> being    <a href="subset_1.html#M1">Element</a> of <font color="Maroon">c<sub>1</sub></font>;<br/>
<a NAME="E2:20_1_1"/><i><font color="Green">E7</font></i>: 
<span class="p1"><a href="pralg_2.html#K7" target="_self">|.</a><span class="default"><span class="p2">(<span class="default"><font color="Maroon">c<sub>3</sub></font> <a href="pralg_2.html#K6" target="_self">.</a> <font color="Maroon">c<sub>5</sub></font></span>)</span></span><a href="pralg_2.html#K7" target="_self">.|</a></span> <a href="hidden.html#R2">in</a> <span class="p1">{<span class="default"> <span class="p2"><a href="pralg_2.html#K7" target="_self">|.</a><span class="default"><span class="p3">(<span class="default"><font color="Maroon">c<sub>3</sub></font> <a href="pralg_2.html#K6" target="_self">.</a> <font color="Olive">b<sub>1</sub></font></span>)</span></span><a href="pralg_2.html#K7" target="_self">.|</a></span> where B is    <a href="subset_1.html#M1">Element</a> of <font color="Maroon">c<sub>1</sub></font> : verum </span>}</span> 
 
;<br/>
<b>consider </b><font color="Maroon">c<sub>6</sub></font> being    <a href="hidden.html#M1">set</a> <b> such that </b><br/><a NAME="E4:20_1_1"/><i><font color="Green">E8</font></i>: 
<font color="Maroon">c<sub>6</sub></font> <a href="hidden.html#R2">in</a> <span class="p1"><a href="pralg_2.html#K7" target="_self">|.</a><span class="default"><span class="p2">(<span class="default"><font color="Maroon">c<sub>3</sub></font> <a href="pralg_2.html#K6" target="_self">.</a> <font color="Maroon">c<sub>5</sub></font></span>)</span></span><a href="pralg_2.html#K7" target="_self">.|</a></span>
 <b>by </b><i><a class="ref" href="xboole_0.html#D1">XBOOLE_0:def 1</a></i>;<br/>
<b>thus </b><a NAME="E5:20_1_1"/>
not <span class="p1"><a href="pralg_2.html#K8" target="_self">|.</a><span class="default"><font color="Maroon">c<sub>3</sub></font></span><a href="pralg_2.html#K8" target="_self">.|</a></span> is <a href="xboole_0.html#V1">empty</a>
 <b>by </b><i><a class="txt" href="pralg_2.html#E2:20_1_1"><i><font color="Green">E7</font></i></a>, <a class="txt" href="pralg_2.html#E4:20_1_1"><i><font color="Green">E8</font></i></a>, <a class="ref" href="tarski.html#D4">TARSKI:def 4</a></i>;<br/>


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