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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/><b>let </b><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>let </b><font color="Maroon">d</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="E1:37"/>
( <font color="Maroon">a</font> <a href="bvfunc_1.html#R1">'&lt;'</a> <font color="Maroon">b</font> &amp; <font color="Maroon">c</font> <a href="bvfunc_1.html#R1">'&lt;'</a> <font color="Maroon">d</font> )
 ;<br/>

<a NAME="E2:37"/><b>then </b>
( <font color="Maroon">a</font> <a href="bvfunc_1.html#K12">'imp'</a> <font color="Maroon">b</font> <a href="funct_2.html#R2">=</a>  <a href="bvfunc_1.html#K17">I_el</a> <font color="Maroon">Y</font> &amp; <font color="Maroon">c</font> <a href="bvfunc_1.html#K12">'imp'</a> <font color="Maroon">d</font> <a href="funct_2.html#R2">=</a>  <a href="bvfunc_1.html#K17">I_el</a> <font color="Maroon">Y</font> )
 
<b>by </b><i><a class="ref" href="bvfunc_1.html#T19">BVFUNC_1:19</a></i>;<br/>
<a NAME="E3:37"/><b>then </b>
<span class="p1">(<span class="default"><font color="Maroon">a</font> <a href="valuat_1.html#K6">'&amp;'</a> <font color="Maroon">c</font></span>)</span> <a href="bvfunc_1.html#K12">'imp'</a> <span class="p1">(<span class="default"><font color="Maroon">b</font> <a href="valuat_1.html#K6">'&amp;'</a> <font color="Maroon">d</font></span>)</span> <a href="funct_2.html#R2">=</a>  <a href="bvfunc_1.html#K17">I_el</a> <font color="Maroon">Y</font>
 
<b>by </b><i><a class="ref" href="bvfunc_6.html#T21">BVFUNC_6:21</a></i>;<br/>
<b>hence </b><a NAME="E4:37"/>
<font color="Maroon">a</font> <a href="valuat_1.html#K6">'&amp;'</a> <font color="Maroon">c</font> <a href="bvfunc_1.html#R1">'&lt;'</a> <font color="Maroon">b</font> <a href="valuat_1.html#K6">'&amp;'</a> <font color="Maroon">d</font>
 <b>by </b><i><a class="ref" href="bvfunc_1.html#T19">BVFUNC_1:19</a></i>;<br/>


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