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<b>let </b><font color="Maroon">G</font> be  non <a href="struct_0.html#V3">empty</a>  <a href="lang1.html#L1">DTConstrStr</a> ;<br/>

<a NAME="E1:16"/><i><font color="Green">E31</font></i>: 
 <a href="lang1.html#K5">Terminals</a> <font color="Maroon">G</font> <a href="hidden.html#R1">=</a> <span class="p1">{<span class="default"> <font color="Olive">t</font> where <font color="Olive">t</font> is   <a href="lang1.html#NM1">Symbol</a> of <font color="Maroon">G</font> : for <font color="Olive">tnt</font> being  <a href="finseq_1.html#NM1">FinSequence</a>  holds not <font color="Olive">t</font> <a href="lang1.html#R1">==&gt;</a> <font color="Olive">tnt</font> </span>}</span> 
 
<b>by </b><i><a class="ref" href="lang1.html#D2">LANG1:def 2</a></i>;<br/>
<a NAME="E2:16"/><i><font color="Green">E32</font></i>: 
 <a href="lang1.html#K6">NonTerminals</a> <font color="Maroon">G</font> <a href="hidden.html#R1">=</a> <span class="p1">{<span class="default"> <font color="Olive">t</font> where <font color="Olive">t</font> is   <a href="lang1.html#NM1">Symbol</a> of <font color="Maroon">G</font> :  ex <font color="Olive">tnt</font> being  <a href="finseq_1.html#NM1">FinSequence</a> st <font color="Olive">t</font> <a href="lang1.html#R1">==&gt;</a> <font color="Olive">tnt</font> </span>}</span> 
 
<b>by </b><i><a class="ref" href="lang1.html#D3">LANG1:def 3</a></i>;<br/>
<b>assume </b><a NAME="E3:16"/>
not  <a href="lang1.html#K5">Terminals</a> <font color="Maroon">G</font> <a href="xboole_0.html#R1">misses</a>  <a href="lang1.html#K6">NonTerminals</a> <font color="Maroon">G</font>
 ;<br/>

<b>then consider </b><font color="Maroon">x</font> being    <a href="hidden.html#M1">set</a> <b> such that </b><br/><a NAME="E5:16"/><i><font color="Green">E34</font></i>: 
( <font color="Maroon">x</font> <a href="hidden.html#R2">in</a>  <a href="lang1.html#K5">Terminals</a> <font color="Maroon">G</font> &amp; <font color="Maroon">x</font> <a href="hidden.html#R2">in</a>  <a href="lang1.html#K6">NonTerminals</a> <font color="Maroon">G</font> )
 <b>by </b><i><a class="ref" href="xboole_0.html#T3">XBOOLE_0:3</a></i>;<br/>
<a NAME="E6:16"/>
(  ex <font color="Olive">t</font> being  <a href="lang1.html#NM1">Symbol</a> of <font color="Maroon">G</font> st <br/>( <font color="Maroon">x</font> <a href="hidden.html#R1">=</a> <font color="Olive">t</font> &amp; ( for <font color="Olive">tnt</font> being  <a href="finseq_1.html#NM1">FinSequence</a>  holds not <font color="Olive">t</font> <a href="lang1.html#R1">==&gt;</a> <font color="Olive">tnt</font> ) ) &amp;  ex <font color="Olive">t</font> being  <a href="lang1.html#NM1">Symbol</a> of <font color="Maroon">G</font> st <br/>( <font color="Maroon">x</font> <a href="hidden.html#R1">=</a> <font color="Olive">t</font> &amp;  ex <font color="Olive">tnt</font> being  <a href="finseq_1.html#NM1">FinSequence</a> st <font color="Olive">t</font> <a href="lang1.html#R1">==&gt;</a> <font color="Olive">tnt</font> ) )
 
<b>by </b><i>, , </i>;<br/>
<b>hence </b><a NAME="E7:16"/>
contradiction
 ;<br/>


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