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<b>consider </b><font color="Maroon">c<sub>1</sub></font> being    <a href="hidden.html#M1">set</a> ;<br/>
<a NAME="E2:7_3_1"/>
<font color="Maroon">c<sub>1</sub></font> <a href="hidden.html#R2">in</a> <span class="p1"><a href="tarski.html#K1">{</a><span class="default"><font color="Maroon">c<sub>1</sub></font></span><a href="tarski.html#K1">}</a></span>
 
<b>by </b><i><a class="ref" href="tarski.html#D1">TARSKI:def 1</a></i>;<br/>
<a NAME="E3:7_3_1"/><b>then </b>
<span class="p1"><a href="tarski.html#K1">{</a><span class="default"><font color="Maroon">c<sub>1</sub></font></span><a href="tarski.html#K1">}</a></span> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a>  <a href="xboole_0.html#K1" target="_self">{}</a> 
 
<b>by </b><i><a class="ref" href="xboole_0.html#D1" target="_self">Def1</a></i>;<br/>
<a NAME="E4:7_3_1"/><b>then </b>
not <span class="p1"><a href="tarski.html#K1">{</a><span class="default"><font color="Maroon">c<sub>1</sub></font></span><a href="tarski.html#K1">}</a></span> is <a href="xboole_0.html#V1" target="_self">empty</a>
 
<b>by </b><i><a class="ref" href="xboole_0.html#D5" target="_self">Def5</a></i>;<br/>
<b>hence </b><a NAME="E5:7_3_1"/>
not for <font color="Olive">b<sub>1</sub></font> being   <a href="hidden.html#M1">set</a>  holds <font color="Olive">b<sub>1</sub></font> is <a href="xboole_0.html#V1" target="_self">empty</a>
 ;<br/>


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