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<b>let </b><font color="Maroon" title="c1">p</font> be    <a href="subset_1.html#M1" title="SUBSET_1:mode.1">Element</a> of  <a href="qc_lang1.html#K8" title="QC_LANG1:func.8">QC-WFF</a> ;<br/><b>let </b><font color="Maroon" title="c2">V</font> be  non <a href="xboole_0.html#V1" title="XBOOLE_0:attr.1">empty</a> <a href="subset_1.html#NM2" title="SUBSET_1:NM.2">Subset</a> of <a href="qc_lang1.html#K1" title="QC_LANG1:func.1">QC-variables</a> ;<br/>



<b>set </b><font color="Maroon" title="c3">p1</font> =  <a href="qc_lang2.html#K13" title="QC_LANG2:func.13">the_left_side_of</a> <font color="Maroon" title="c1">p</font>;<br/>
<b>set </b><font color="Maroon" title="c4">p2</font> =  <a href="qc_lang2.html#K14" title="QC_LANG2:func.14">the_right_side_of</a> <font color="Maroon" title="c1">p</font>;<br/>
<b>assume </b><a NAME="E1:55"/>
<font color="Maroon" title="c1">p</font> is <a href="qc_lang2.html#V3" title="QC_LANG2:attr.3">biconditional</a>
 ;<br/>

<a NAME="E2:55"/><b>then </b>
<font color="Maroon" title="c1">p</font> <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a> <span class="p1">(<span class="default"><a href="qc_lang2.html#K13" title="QC_LANG2:func.13">the_left_side_of</a> <font color="Maroon" title="c1">p</font></span>)</span> <a href="qc_lang2.html#K4" title="QC_LANG2:func.4">&lt;=&gt;</a> <span class="p1">(<span class="default"><a href="qc_lang2.html#K14" title="QC_LANG2:func.14">the_right_side_of</a> <font color="Maroon" title="c1">p</font></span>)</span>
 
<b>by </b><i><a class="ref" href="qc_lang2.html#T55" title="QC_LANG2:th.55">QC_LANG2:55</a></i>;<br/>
<a NAME="E3:55"/><b>then </b>
<font color="Maroon" title="c1">p</font> <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a> <span class="p1">(<span class="default"><span class="p2">(<span class="default"><a href="qc_lang2.html#K13" title="QC_LANG2:func.13">the_left_side_of</a> <font color="Maroon" title="c1">p</font></span>)</span> <a href="qc_lang2.html#K2" title="QC_LANG2:func.2">=&gt;</a> <span class="p2">(<span class="default"><a href="qc_lang2.html#K14" title="QC_LANG2:func.14">the_right_side_of</a> <font color="Maroon" title="c1">p</font></span>)</span></span>)</span> <a href="qc_lang1.html#K13" title="QC_LANG1:func.13">'&amp;'</a> <span class="p1">(<span class="default"><span class="p2">(<span class="default"><a href="qc_lang2.html#K14" title="QC_LANG2:func.14">the_right_side_of</a> <font color="Maroon" title="c1">p</font></span>)</span> <a href="qc_lang2.html#K2" title="QC_LANG2:func.2">=&gt;</a> <span class="p2">(<span class="default"><a href="qc_lang2.html#K13" title="QC_LANG2:func.13">the_left_side_of</a> <font color="Maroon" title="c1">p</font></span>)</span></span>)</span>
 
<b>by </b><i><a class="ref" href="qc_lang2.html#D4" title="QC_LANG2:def.4">QC_LANG2:def 4</a></i>;<br/>
<b>hence </b> <a href="qc_lang3.html#K4" title="QC_LANG3:func.4">Vars</a> <font color="Maroon" title="c1">p</font>,<font color="Maroon" title="c2">V</font> = 
<span class="p1">(<span class="default"><a href="qc_lang3.html#K4" title="QC_LANG3:func.4">Vars</a> <span class="p2">(<span class="default"><span class="p3">(<span class="default"><a href="qc_lang2.html#K13" title="QC_LANG2:func.13">the_left_side_of</a> <font color="Maroon" title="c1">p</font></span>)</span> <a href="qc_lang2.html#K2" title="QC_LANG2:func.2">=&gt;</a> <span class="p3">(<span class="default"><a href="qc_lang2.html#K14" title="QC_LANG2:func.14">the_right_side_of</a> <font color="Maroon" title="c1">p</font></span>)</span></span>)</span>,<font color="Maroon" title="c2">V</font></span>)</span> <a href="subset_1.html#K4" title="SUBSET_1:func.4">\/</a> <span class="p1">(<span class="default"><a href="qc_lang3.html#K4" title="QC_LANG3:func.4">Vars</a> <span class="p2">(<span class="default"><span class="p3">(<span class="default"><a href="qc_lang2.html#K14" title="QC_LANG2:func.14">the_right_side_of</a> <font color="Maroon" title="c1">p</font></span>)</span> <a href="qc_lang2.html#K2" title="QC_LANG2:func.2">=&gt;</a> <span class="p3">(<span class="default"><a href="qc_lang2.html#K13" title="QC_LANG2:func.13">the_left_side_of</a> <font color="Maroon" title="c1">p</font></span>)</span></span>)</span>,<font color="Maroon" title="c2">V</font></span>)</span>
<b>by </b><i><a class="ref" href="qc_lang3.html#T53" target="_self" title="QC_LANG3:th.53">Th53</a></i>
<br/>.= 
<span class="p1">(<span class="default"><span class="p2">(<span class="default"><a href="qc_lang3.html#K4" title="QC_LANG3:func.4">Vars</a> <span class="p3">(<span class="default"><a href="qc_lang2.html#K13" title="QC_LANG2:func.13">the_left_side_of</a> <font color="Maroon" title="c1">p</font></span>)</span>,<font color="Maroon" title="c2">V</font></span>)</span> <a href="subset_1.html#K4" title="SUBSET_1:func.4">\/</a> <span class="p2">(<span class="default"><a href="qc_lang3.html#K4" title="QC_LANG3:func.4">Vars</a> <span class="p3">(<span class="default"><a href="qc_lang2.html#K14" title="QC_LANG2:func.14">the_right_side_of</a> <font color="Maroon" title="c1">p</font></span>)</span>,<font color="Maroon" title="c2">V</font></span>)</span></span>)</span> <a href="subset_1.html#K4" title="SUBSET_1:func.4">\/</a> <span class="p1">(<span class="default"><a href="qc_lang3.html#K4" title="QC_LANG3:func.4">Vars</a> <span class="p2">(<span class="default"><span class="p3">(<span class="default"><a href="qc_lang2.html#K14" title="QC_LANG2:func.14">the_right_side_of</a> <font color="Maroon" title="c1">p</font></span>)</span> <a href="qc_lang2.html#K2" title="QC_LANG2:func.2">=&gt;</a> <span class="p3">(<span class="default"><a href="qc_lang2.html#K13" title="QC_LANG2:func.13">the_left_side_of</a> <font color="Maroon" title="c1">p</font></span>)</span></span>)</span>,<font color="Maroon" title="c2">V</font></span>)</span>
<b>by </b><i><a class="ref" href="qc_lang3.html#T59" target="_self" title="QC_LANG3:th.59">Th59</a></i>
<br/>.= 
<span class="p1">(<span class="default"><span class="p2">(<span class="default"><a href="qc_lang3.html#K4" title="QC_LANG3:func.4">Vars</a> <span class="p3">(<span class="default"><a href="qc_lang2.html#K13" title="QC_LANG2:func.13">the_left_side_of</a> <font color="Maroon" title="c1">p</font></span>)</span>,<font color="Maroon" title="c2">V</font></span>)</span> <a href="subset_1.html#K4" title="SUBSET_1:func.4">\/</a> <span class="p2">(<span class="default"><a href="qc_lang3.html#K4" title="QC_LANG3:func.4">Vars</a> <span class="p3">(<span class="default"><a href="qc_lang2.html#K14" title="QC_LANG2:func.14">the_right_side_of</a> <font color="Maroon" title="c1">p</font></span>)</span>,<font color="Maroon" title="c2">V</font></span>)</span></span>)</span> <a href="subset_1.html#K4" title="SUBSET_1:func.4">\/</a> <span class="p1">(<span class="default"><span class="p2">(<span class="default"><a href="qc_lang3.html#K4" title="QC_LANG3:func.4">Vars</a> <span class="p3">(<span class="default"><a href="qc_lang2.html#K13" title="QC_LANG2:func.13">the_left_side_of</a> <font color="Maroon" title="c1">p</font></span>)</span>,<font color="Maroon" title="c2">V</font></span>)</span> <a href="subset_1.html#K4" title="SUBSET_1:func.4">\/</a> <span class="p2">(<span class="default"><a href="qc_lang3.html#K4" title="QC_LANG3:func.4">Vars</a> <span class="p3">(<span class="default"><a href="qc_lang2.html#K14" title="QC_LANG2:func.14">the_right_side_of</a> <font color="Maroon" title="c1">p</font></span>)</span>,<font color="Maroon" title="c2">V</font></span>)</span></span>)</span>
<b>by </b><i><a class="ref" href="qc_lang3.html#T59" target="_self" title="QC_LANG3:th.59">Th59</a></i>
<br/>.= 
<span class="p1">(<span class="default"><a href="qc_lang3.html#K4" title="QC_LANG3:func.4">Vars</a> <span class="p2">(<span class="default"><a href="qc_lang2.html#K13" title="QC_LANG2:func.13">the_left_side_of</a> <font color="Maroon" title="c1">p</font></span>)</span>,<font color="Maroon" title="c2">V</font></span>)</span> <a href="subset_1.html#K4" title="SUBSET_1:func.4">\/</a> <span class="p1">(<span class="default"><a href="qc_lang3.html#K4" title="QC_LANG3:func.4">Vars</a> <span class="p2">(<span class="default"><a href="qc_lang2.html#K14" title="QC_LANG2:func.14">the_right_side_of</a> <font color="Maroon" title="c1">p</font></span>)</span>,<font color="Maroon" title="c2">V</font></span>)</span>

;<br/><br/>


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