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<b>let </b><font color="Maroon" title="c1">F</font>, <font color="Maroon" title="c2">G</font> be   <a href="zf_lang.html#NM2" title="ZF_LANG:NM.2">ZF-formula</a>;<br/>



<b>assume </b><a NAME="E1:29"/>
<font color="Maroon" title="c1">F</font> <a href="zf_lang.html#R2" title="ZF_LANG:pred.2">is_subformula_of</a> <font color="Maroon" title="c2">G</font>
 ;<br/>

<a NAME="E2:29"/><b>then </b>
( <font color="Maroon" title="c1">F</font> <a href="zf_lang.html#R3" title="ZF_LANG:pred.3">is_proper_subformula_of</a> <font color="Maroon" title="c2">G</font> or <font color="Maroon" title="c1">F</font> <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a> <font color="Maroon" title="c2">G</font> )
 
<b>by </b><i><a class="ref" href="zf_lang.html#D41" title="ZF_LANG:def.41">ZF_LANG:def 41</a></i>;<br/>
<b>hence </b><a NAME="E3:29"/>
 <a href="finseq_1.html#K3" title="FINSEQ_1:func.3">len</a> <font color="Maroon" title="c1">F</font> <a href="xxreal_0.html#R1" title="XXREAL_0:pred.1">&lt;=</a>  <a href="finseq_1.html#K3" title="FINSEQ_1:func.3">len</a> <font color="Maroon" title="c2">G</font>
 <b>by </b><i><a class="ref" href="zf_lang.html#T83" title="ZF_LANG:th.83">ZF_LANG:83</a></i>;<br/>


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