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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#M1">Element</a> of  <a href="qc_lang1.html#K8">QC-WFF</a> ;<br/>



<b>assume </b><a NAME="E1:82"/>
<font color="Maroon">c<sub>1</sub></font> <a href="hidden.html#R2">in</a>  <a href="qc_lang2.html#K15" target="_self">Subformulae</a> <font color="Maroon">c<sub>2</sub></font>
 ;<br/>

<a NAME="E2:82"/><b>then </b>
<font color="Maroon">c<sub>1</sub></font> <a href="qc_lang2.html#R2" target="_self">is_subformula_of</a> <font color="Maroon">c<sub>2</sub></font>
 
<b>by </b><i><a class="ref" href="qc_lang2.html#T103" target="_self">Th103</a></i>;<br/>
<b>hence </b><a NAME="E3:82"/>
 <a href="qc_lang2.html#K15" target="_self">Subformulae</a> <font color="Maroon">c<sub>1</sub></font> <a href="tarski.html#R1">c=</a>  <a href="qc_lang2.html#K15" target="_self">Subformulae</a> <font color="Maroon">c<sub>2</sub></font>
 <b>by </b><i><a class="ref" href="qc_lang2.html#T104" target="_self">Th104</a></i>;<br/>


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