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<b>let </b><font color="Maroon">V</font> be  non <a href="xboole_0.html#V1">empty</a>  <a href="hidden.html#M1">set</a> ;<br/><b>let </b><font color="Maroon">A</font> be    <a href="subset_1.html#M1">Element</a> of <font color="Maroon">V</font>;<br/><b>let </b><font color="Maroon">B</font> be    <a href="subset_1.html#M1">Element</a> of <font color="Maroon">V</font>;<br/><b>let </b><font color="Maroon">x</font> be    <a href="hidden.html#M1">set</a> ; <i><font color="Red">:: according to </font></i><a class="ref" href="tarski.html#D3">TARSKI:def 3</a><br/>







<b>assume </b><a NAME="E1:4"/>
<font color="Maroon">x</font> <a href="hidden.html#R2">in</a>  <a href="funct_2.html#K1">Funcs</a> <font color="Maroon">A</font>,<font color="Maroon">B</font>
 ;<br/>

<a NAME="E2:4"/><b>then </b>
( ( <font color="Maroon">B</font> <a href="hidden.html#R1">=</a>  <a href="xboole_0.html#K1">{}</a>  implies <font color="Maroon">A</font> <a href="hidden.html#R1">=</a>  <a href="xboole_0.html#K1">{}</a>  ) &amp; <font color="Maroon">x</font> is   <a href="funct_2.html#NM1">Function</a> of <font color="Maroon">A</font>,<font color="Maroon">B</font> )
 
<b>by </b><i><a class="ref" href="funct_2.html#T14">FUNCT_2:14</a>, <a class="ref" href="funct_2.html#T121">FUNCT_2:121</a></i>;<br/>
<b>hence </b><a NAME="E3:4"/>
<font color="Maroon">x</font> <a href="hidden.html#R2">in</a>  <a href="ens_1.html#K1" target="_self">Funcs</a> <font color="Maroon">V</font>
 <b>by </b><i/>;<br/>


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