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<b>let </b><font color="Maroon">p</font> be   <a href="qc_lang1.html#NM8">QC-formula</a>, <font color="Maroon">q</font> be   <a href="qc_lang1.html#NM8">QC-formula</a>;<br/>

<a NAME="E1:25"/>
( <font color="Maroon">p</font> <a href="qc_lang2.html#K4">&lt;=&gt;</a> <font color="Maroon">q</font> is <a href="qc_lang2.html#V3">biconditional</a> &amp;  <a href="qc_lang2.html#K13">the_left_side_of</a> <span class="p1">(<span class="default"><font color="Maroon">p</font> <a href="qc_lang2.html#K4">&lt;=&gt;</a> <font color="Maroon">q</font></span>)</span> <a href="hidden.html#R1">=</a> <font color="Maroon">p</font> &amp;  <a href="qc_lang2.html#K14">the_right_side_of</a> <span class="p1">(<span class="default"><font color="Maroon">p</font> <a href="qc_lang2.html#K4">&lt;=&gt;</a> <font color="Maroon">q</font></span>)</span> <a href="hidden.html#R1">=</a> <font color="Maroon">q</font> )
 
<b>by </b><i><a class="ref" href="qc_lang2.html#T47">QC_LANG2:47</a>, <a class="ref" href="qc_lang2.html#D12">QC_LANG2:def 12</a></i>;<br/>
<b>hence </b><a NAME="E2:25"/>
 <a href="qc_lang1.html#K23">still_not-bound_in</a> <span class="p1">(<span class="default"><font color="Maroon">p</font> <a href="qc_lang2.html#K4">&lt;=&gt;</a> <font color="Maroon">q</font></span>)</span> <a href="hidden.html#R1">=</a> <span class="p1">(<span class="default"><a href="qc_lang1.html#K23">still_not-bound_in</a> <font color="Maroon">p</font></span>)</span> <a href="subset_1.html#K4">\/</a> <span class="p1">(<span class="default"><a href="qc_lang1.html#K23">still_not-bound_in</a> <font color="Maroon">q</font></span>)</span>
 <b>by </b><i/>;<br/>


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