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<b>let </b><font color="Maroon">Y</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="fraenkel.html#M2">Element</a> of  <a href="fraenkel.html#K1">Funcs</a> <font color="Maroon">Y</font>,<a href="margrel1.html#K6">BOOLEAN</a> ;<br/><b>let </b><font color="Maroon">b</font> be    <a href="fraenkel.html#M2">Element</a> of  <a href="fraenkel.html#K1">Funcs</a> <font color="Maroon">Y</font>,<a href="margrel1.html#K6">BOOLEAN</a> ;<br/>





<a NAME="E1:3"/>
<span class="p1">(<span class="default"><span class="p2">(<span class="default"><a href="valuat_1.html#K5">'not'</a> <font color="Maroon">b</font></span>)</span> <a href="bvfunc_1.html#K12">'imp'</a> <span class="p2">(<span class="default"><a href="valuat_1.html#K5">'not'</a> <font color="Maroon">a</font></span>)</span></span>)</span> <a href="bvfunc_1.html#K12">'imp'</a> <span class="p1">(<span class="default"><font color="Maroon">a</font> <a href="bvfunc_1.html#K12">'imp'</a> <font color="Maroon">b</font></span>)</span> <a href="hidden.html#R1">=</a>  <a href="bvfunc_1.html#K17">I_el</a> <font color="Maroon">Y</font>
 
<b>by </b><i/>;<br/>
<a NAME="E2:3"/><b>then </b><i><font color="Green">E17</font></i>: 
<span class="p1">(<span class="default"><a href="valuat_1.html#K5">'not'</a> <font color="Maroon">b</font></span>)</span> <a href="bvfunc_1.html#K12">'imp'</a> <span class="p1">(<span class="default"><a href="valuat_1.html#K5">'not'</a> <font color="Maroon">a</font></span>)</span> <a href="bvfunc_1.html#R1">'&lt;'</a> <font color="Maroon">a</font> <a href="bvfunc_1.html#K12">'imp'</a> <font color="Maroon">b</font>
 
<b>by </b><i><a class="ref" href="bvfunc_1.html#T19">BVFUNC_1:19</a></i>;<br/>
<a NAME="E3:3"/>
<span class="p1">(<span class="default"><font color="Maroon">a</font> <a href="bvfunc_1.html#K12">'imp'</a> <font color="Maroon">b</font></span>)</span> <a href="bvfunc_1.html#K12">'imp'</a> <span class="p1">(<span class="default"><span class="p2">(<span class="default"><a href="valuat_1.html#K5">'not'</a> <font color="Maroon">b</font></span>)</span> <a href="bvfunc_1.html#K12">'imp'</a> <span class="p2">(<span class="default"><a href="valuat_1.html#K5">'not'</a> <font color="Maroon">a</font></span>)</span></span>)</span> <a href="hidden.html#R1">=</a>  <a href="bvfunc_1.html#K17">I_el</a> <font color="Maroon">Y</font>
 
<b>by </b><i><a class="ref" href="bvfunc_5.html#T33">BVFUNC_5:33</a></i>;<br/>
<a NAME="E4:3"/><b>then </b>
<font color="Maroon">a</font> <a href="bvfunc_1.html#K12">'imp'</a> <font color="Maroon">b</font> <a href="bvfunc_1.html#R1">'&lt;'</a> <span class="p1">(<span class="default"><a href="valuat_1.html#K5">'not'</a> <font color="Maroon">b</font></span>)</span> <a href="bvfunc_1.html#K12">'imp'</a> <span class="p1">(<span class="default"><a href="valuat_1.html#K5">'not'</a> <font color="Maroon">a</font></span>)</span>
 
<b>by </b><i><a class="ref" href="bvfunc_1.html#T19">BVFUNC_1:19</a></i>;<br/>
<b>hence </b><a NAME="E5:3"/>
<font color="Maroon">a</font> <a href="bvfunc_1.html#K12">'imp'</a> <font color="Maroon">b</font> <a href="hidden.html#R1">=</a> <span class="p1">(<span class="default"><a href="valuat_1.html#K5">'not'</a> <font color="Maroon">b</font></span>)</span> <a href="bvfunc_1.html#K12">'imp'</a> <span class="p1">(<span class="default"><a href="valuat_1.html#K5">'not'</a> <font color="Maroon">a</font></span>)</span>
 <b>by </b><i>, <a class="ref" href="bvfunc_1.html#T18">BVFUNC_1:18</a></i>;<br/>


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