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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="subset_1.html#M2">Element</a> of  <a href="cqc_lang.html#K7">CQC-WFF</a> ;<br/>



<b>assume </b><b>that </b><br/><a NAME="E1:52"/><i><font color="Green">E43</font></i>: 
<font color="Maroon">c<sub>1</sub></font> is <a href="qc_lang1.html#V6">closed</a>
 <b>and </b><br/><a NAME="E2:52"/><i><font color="Green">E44</font></i>: 
 <a href="cqc_lang.html#K10">'not'</a> <font color="Maroon">c<sub>1</sub></font> <a href="cqc_the3.html#R1" target="_self">|-</a>  <a href="cqc_lang.html#K10">'not'</a> <font color="Maroon">c<sub>2</sub></font>
 ;<br/>

<a NAME="E3:52"/>
 <a href="cqc_lang.html#K10">'not'</a> <font color="Maroon">c<sub>1</sub></font> is <a href="qc_lang1.html#V6">closed</a>
 
<b>by </b><i><a class="txt" href="cqc_the3.html#E1:52"><i><font color="Green">E43</font></i></a>, <a class="ref" href="qc_lang3.html#T25">QC_LANG3:25</a></i>;<br/>
<a NAME="E4:52"/><b>then </b>
<span class="p1">(<span class="default"><a href="cqc_lang.html#K10">'not'</a> <font color="Maroon">c<sub>1</sub></font></span>)</span> <a href="cqc_lang.html#K12">=&gt;</a> <span class="p1">(<span class="default"><a href="cqc_lang.html#K10">'not'</a> <font color="Maroon">c<sub>2</sub></font></span>)</span> is <a href="cqc_the1.html#V2">valid</a>
 
<b>by </b><i><a class="txt" href="cqc_the3.html#E2:52"><i><font color="Green">E44</font></i></a>, <a class="ref" href="cqc_the3.html#T41" target="_self">Th41</a></i>;<br/>
<a NAME="E5:52"/><b>then </b>
<font color="Maroon">c<sub>2</sub></font> <a href="cqc_lang.html#K12">=&gt;</a> <font color="Maroon">c<sub>1</sub></font> is <a href="cqc_the1.html#V2">valid</a>
 
<b>by </b><i><a class="ref" href="lukasi_1.html#T63">LUKASI_1:63</a></i>;<br/>
<b>hence </b><a NAME="E6:52"/>
<font color="Maroon">c<sub>2</sub></font> <a href="cqc_the3.html#R1" target="_self">|-</a> <font color="Maroon">c<sub>1</sub></font>
 <b>by </b><i><a class="ref" href="cqc_the3.html#T39" target="_self">Th39</a></i>;<br/>


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