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<b>let </b><font color="Maroon">p</font> be    <a href="subset_1.html#M2">Element</a> of  <a href="cqc_lang.html#K7">CQC-WFF</a> ;<br/><b>let </b><font color="Maroon">q</font> be    <a href="subset_1.html#M2">Element</a> of  <a href="cqc_lang.html#K7">CQC-WFF</a> ;<br/><b>let </b><font color="Maroon">x</font> be   <a href="qc_lang1.html#NM3">bound_QC-variable</a>;<br/>





<b>assume </b><a NAME="E1:67"/>
<font color="Maroon">p</font> <a href="cqc_the3.html#R7" target="_self">&lt;==&gt;</a> <font color="Maroon">q</font>
 ;<br/>

<a NAME="E2:67"/><b>then </b>
 <a href="cqc_lang.html#K10">'not'</a> <font color="Maroon">p</font> <a href="cqc_the3.html#R7" target="_self">&lt;==&gt;</a>  <a href="cqc_lang.html#K10">'not'</a> <font color="Maroon">q</font>
 
<b>by </b><i><a class="ref" href="cqc_the3.html#T5" target="_self">Th5</a></i>;<br/>
<a NAME="E3:67"/><b>then </b>
 <a href="cqc_lang.html#K15">All</a> <font color="Maroon">x</font>,<span class="p1">(<span class="default"><a href="cqc_lang.html#K10">'not'</a> <font color="Maroon">p</font></span>)</span> <a href="cqc_the3.html#R7" target="_self">&lt;==&gt;</a>  <a href="cqc_lang.html#K15">All</a> <font color="Maroon">x</font>,<span class="p1">(<span class="default"><a href="cqc_lang.html#K10">'not'</a> <font color="Maroon">q</font></span>)</span>
 
<b>by </b><i/>;<br/>
<a NAME="E4:67"/><b>then </b><i><font color="Green">E39</font></i>: 
 <a href="cqc_lang.html#K10">'not'</a> <span class="p1">(<span class="default"><a href="cqc_lang.html#K15">All</a> <font color="Maroon">x</font>,<span class="p2">(<span class="default"><a href="cqc_lang.html#K10">'not'</a> <font color="Maroon">p</font></span>)</span></span>)</span> <a href="cqc_the3.html#R7" target="_self">&lt;==&gt;</a>  <a href="cqc_lang.html#K10">'not'</a> <span class="p1">(<span class="default"><a href="cqc_lang.html#K15">All</a> <font color="Maroon">x</font>,<span class="p2">(<span class="default"><a href="cqc_lang.html#K10">'not'</a> <font color="Maroon">q</font></span>)</span></span>)</span>
 
<b>by </b><i><a class="ref" href="cqc_the3.html#T5" target="_self">Th5</a></i>;<br/>
<a NAME="E5:67"/>
 <a href="cqc_lang.html#K16">Ex</a> <font color="Maroon">x</font>,<font color="Maroon">p</font> <a href="hidden.html#R1">=</a>  <a href="cqc_lang.html#K10">'not'</a> <span class="p1">(<span class="default"><a href="cqc_lang.html#K15">All</a> <font color="Maroon">x</font>,<span class="p2">(<span class="default"><a href="cqc_lang.html#K10">'not'</a> <font color="Maroon">p</font></span>)</span></span>)</span>
 
<b>by </b><i><a class="ref" href="qc_lang2.html#D5">QC_LANG2:def 5</a></i>;<br/>
<b>hence </b><a NAME="E6:67"/>
 <a href="cqc_lang.html#K16">Ex</a> <font color="Maroon">x</font>,<font color="Maroon">p</font> <a href="cqc_the3.html#R7" target="_self">&lt;==&gt;</a>  <a href="cqc_lang.html#K16">Ex</a> <font color="Maroon">x</font>,<font color="Maroon">q</font>
 <b>by </b><i><a class="ref" href="cqc_the3.html#T9" target="_self">Th9</a>, <a class="ref" href="qc_lang2.html#D5">QC_LANG2:def 5</a></i>;<br/>


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