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<b>let </b><font color="Maroon" title="c1">IT</font> be    <a href="hidden.html#M1" title="HIDDEN:mode.1">set</a> ;<br/>

<b>assume </b><a NAME="E1:11_3_1"/>
( not <font color="Maroon" title="c1">IT</font> is <a href="xboole_0.html#V1" title="XBOOLE_0:attr.1">empty</a> &amp; ( for <font color="Olive" title="b1">x</font> being   <a href="hidden.html#M1" title="HIDDEN:mode.1">set</a>   holds not <font color="Maroon" title="c1">IT</font> <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a> <span class="p1"><a href="tarski.html#K1" title="TARSKI:func.1">{</a><span class="default"><font color="Olive" title="b1">x</font></span><a href="tarski.html#K1" title="TARSKI:func.1">}</a></span> ) )
 ; <i><font color="Red">:: according to </font></i><a class="ref" href="realset1.html#D4" target="_self" title="REALSET1:def.4">REALSET1:def 4</a><br/>

<b>hence </b><a NAME="E2:11_3_1"/>
not <font color="Maroon" title="c1">IT</font> is <a href="xboole_0.html#V1" title="XBOOLE_0:attr.1">empty</a>
 ;<br/>


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