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<b>let </b><font color="Maroon">G</font> be    <a href="subset_1.html#M1">Element</a> of  <a href="qc_lang1.html#K8">QC-WFF</a> ;<br/><b>let </b><font color="Maroon">H</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="E1:80"/>
<font color="Maroon">G</font> <a href="hidden.html#R2">in</a>  <a href="qc_lang2.html#K15" target="_self">Subformulae</a> <font color="Maroon">H</font>
 ;<br/>

<a NAME="E2:80"/><b>then </b>
 ex <font color="Olive">F</font> being   <a href="subset_1.html#M1">Element</a> of  <a href="qc_lang1.html#K8">QC-WFF</a>  st <br/>( <font color="Olive">F</font> <a href="hidden.html#R1">=</a> <font color="Maroon">G</font> &amp; <font color="Olive">F</font> <a href="qc_lang2.html#R2" target="_self">is_subformula_of</a> <font color="Maroon">H</font> )
 
<b>by </b><i/>;<br/>
<b>hence </b><a NAME="E3:80"/>
<font color="Maroon">G</font> <a href="qc_lang2.html#R2" target="_self">is_subformula_of</a> <font color="Maroon">H</font>
 ;<br/>


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