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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="E1:57"/><i><font color="Green">E28</font></i>: 
( <font color="Maroon">G</font> <a href="qc_lang2.html#R2" target="_self">is_subformula_of</a> <font color="Maroon">H</font> &amp; <font color="Maroon">H</font> <a href="qc_lang2.html#R2" target="_self">is_subformula_of</a> <font color="Maroon">G</font> )
 ;<br/>

<b>assume </b><a NAME="E2:57"/>
<font color="Maroon">G</font> <a href="hidden.html#NR2" target="_self">&lt;&gt;</a> <font color="Maroon">H</font>
 ;<br/>

<a NAME="E3:57"/><b>then </b>
( <font color="Maroon">G</font> <a href="qc_lang2.html#R3" target="_self">is_proper_subformula_of</a> <font color="Maroon">H</font> &amp; <font color="Maroon">H</font> <a href="qc_lang2.html#R3" target="_self">is_proper_subformula_of</a> <font color="Maroon">G</font> )
 
<b>by </b><i>, <a class="ref" href="qc_lang2.html#T4" target="_self">Th4</a></i>;<br/>
<a NAME="E4:57"/><b>then </b>
(  <a href="finseq_1.html#K3">len</a> <span class="p1">(<span class="default"><a href="qc_lang1.html#K10">@</a> <font color="Maroon">G</font></span>)</span> <a href="xxreal_0.html#NR3" target="_self">&lt;</a>  <a href="finseq_1.html#K3">len</a> <span class="p1">(<span class="default"><a href="qc_lang1.html#K10">@</a> <font color="Maroon">H</font></span>)</span> &amp;  <a href="finseq_1.html#K3">len</a> <span class="p1">(<span class="default"><a href="qc_lang1.html#K10">@</a> <font color="Maroon">H</font></span>)</span> <a href="xxreal_0.html#NR3" target="_self">&lt;</a>  <a href="finseq_1.html#K3">len</a> <span class="p1">(<span class="default"><a href="qc_lang1.html#K10">@</a> <font color="Maroon">G</font></span>)</span> )
 
<b>by </b><i><a class="ref" href="qc_lang2.html#T7" target="_self">Th7</a></i>;<br/>
<b>hence </b><a NAME="E5:57"/>
contradiction
 ;<br/>


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