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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> , <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> , <font color="Maroon">c</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>assume </b><a NAME="E1:28"/>
( <font color="Maroon">a</font> <a href="bvfunc_1.html#K12">'imp'</a> <span class="p1">(<span class="default"><font color="Maroon">b</font> <a href="bvfunc_1.html#K12">'imp'</a> <font color="Maroon">c</font></span>)</span> <a href="hidden.html#R1">=</a>  <a href="bvfunc_1.html#K17">I_el</a> <font color="Maroon">Y</font> &amp; <font color="Maroon">a</font> <a href="bvfunc_1.html#K12">'imp'</a> <font color="Maroon">b</font> <a href="hidden.html#R1">=</a>  <a href="bvfunc_1.html#K17">I_el</a> <font color="Maroon">Y</font> )
 ;<br/>

<a NAME="E2:28"/><b>then </b>
<span class="p1">(<span class="default"><a href="bvfunc_1.html#K17">I_el</a> <font color="Maroon">Y</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="bvfunc_1.html#K17">I_el</a> <font color="Maroon">Y</font></span>)</span> <a href="bvfunc_1.html#K12">'imp'</a> <span class="p2">(<span class="default"><font color="Maroon">a</font> <a href="bvfunc_1.html#K12">'imp'</a> <font color="Maroon">c</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/>;<br/>
<b>hence </b><a NAME="E3:28"/>
<font color="Maroon">a</font> <a href="bvfunc_1.html#K12">'imp'</a> <font color="Maroon">c</font> <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/>


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