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<b>let </b><font color="Maroon">c<sub>1</sub></font>, <font color="Maroon">c<sub>2</sub></font> be   <a href="qc_lang1.html#NM8">QC-formula</a>;<br/>

<b>set </b><font color="Maroon">c<sub>3</sub></font> = <font color="Maroon">c<sub>1</sub></font> <a href="qc_lang1.html#K13">'&amp;'</a> <font color="Maroon">c<sub>2</sub></font>;<br/>
<a NAME="E1:17"/><i><font color="Green">E9</font></i>: 
<font color="Maroon">c<sub>1</sub></font> <a href="qc_lang1.html#K13">'&amp;'</a> <font color="Maroon">c<sub>2</sub></font> is <a href="qc_lang1.html#V4">conjunctive</a>
 
<b>by </b><i><a class="ref" href="qc_lang1.html#D19">QC_LANG1:def 19</a></i>;<br/>
<a NAME="E2:17"/><b>then </b>
(  <a href="qc_lang1.html#K18">the_left_argument_of</a> <span class="p1">(<span class="default"><font color="Maroon">c<sub>1</sub></font> <a href="qc_lang1.html#K13">'&amp;'</a> <font color="Maroon">c<sub>2</sub></font></span>)</span> <a href="hidden.html#R1">=</a> <font color="Maroon">c<sub>1</sub></font> &amp;  <a href="qc_lang1.html#K19">the_right_argument_of</a> <span class="p1">(<span class="default"><font color="Maroon">c<sub>1</sub></font> <a href="qc_lang1.html#K13">'&amp;'</a> <font color="Maroon">c<sub>2</sub></font></span>)</span> <a href="hidden.html#R1">=</a> <font color="Maroon">c<sub>2</sub></font> )
 
<b>by </b><i><a class="ref" href="qc_lang1.html#D24">QC_LANG1:def 24</a>, <a class="ref" href="qc_lang1.html#D25">QC_LANG1:def 25</a></i>;<br/>
<b>hence </b><a NAME="E3:17"/>
 <a href="qc_lang1.html#K23">still_not-bound_in</a> <span class="p1">(<span class="default"><font color="Maroon">c<sub>1</sub></font> <a href="qc_lang1.html#K13">'&amp;'</a> <font color="Maroon">c<sub>2</sub></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">c<sub>1</sub></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">c<sub>2</sub></font></span>)</span>
 <b>by </b><i><a class="txt" href="qc_lang3.html#E1:17"><i><font color="Green">E9</font></i></a>, <a class="ref" href="qc_lang3.html#T13" target="_self">Th13</a></i>;<br/>


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