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<b>let </b><font color="Maroon" title="c1">E</font> be    <a href="hidden.html#M1" title="HIDDEN:mode.1">set</a> ;<br/><b>let </b><font color="Maroon" title="c2">S</font>, <font color="Maroon" title="c3">T</font> be   <a href="rewrite2.html#NM1" title="REWRITE2:NM.1">semi-Thue-system</a> of <font color="Maroon" title="c1">E</font>;<br/><b>let </b><font color="Maroon" title="c4">s</font>, <font color="Maroon" title="c5">t</font> be    <a href="catalan2.html#M2" title="CATALAN2:mode.2">Element</a> of <font color="Maroon" title="c1">E</font> <a href="catalan2.html#K3" title="CATALAN2:func.3">^omega</a> ;<br/>









<b>assume </b><a NAME="E1:38"/><i><font color="Green" title="E20">A</font></i>: 
( <font color="Maroon" title="c2">S</font> <a href="relset_1.html#R1" title="RELSET_1:pred.1">c=</a> <font color="Maroon" title="c3">T</font> &amp; <font color="Maroon" title="c4">s</font> <a href="rewrite2.html#R2" title="REWRITE2:pred.2">==&gt;.</a> <font color="Maroon" title="c5">t</font>,<font color="Maroon" title="c2">S</font> )
 ;<br/>

<b>then consider </b><font color="Maroon" title="c6">v</font>, <font color="Maroon" title="c7">w</font>, <font color="Maroon" title="c8">s1</font>, <font color="Maroon" title="c9">t1</font> being    <a href="catalan2.html#M2" title="CATALAN2:mode.2">Element</a> of <font color="Maroon" title="c1">E</font> <a href="catalan2.html#K3" title="CATALAN2:func.3">^omega</a> <b> such that </b><br/><a NAME="E3:38"/><i><font color="Green" title="E21">B</font></i>: 
( <font color="Maroon" title="c4">s</font> <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a> <span class="p1">(<span class="default"><font color="Maroon" title="c6">v</font> <a href="flang_1.html#K1" title="FLANG_1:func.1">^</a> <font color="Maroon" title="c8">s1</font></span>)</span> <a href="flang_1.html#K1" title="FLANG_1:func.1">^</a> <font color="Maroon" title="c7">w</font> &amp; <font color="Maroon" title="c5">t</font> <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a> <span class="p1">(<span class="default"><font color="Maroon" title="c6">v</font> <a href="flang_1.html#K1" title="FLANG_1:func.1">^</a> <font color="Maroon" title="c9">t1</font></span>)</span> <a href="flang_1.html#K1" title="FLANG_1:func.1">^</a> <font color="Maroon" title="c7">w</font> &amp; <font color="Maroon" title="c8">s1</font> <a href="rewrite2.html#R1" title="REWRITE2:pred.1">--&gt;.</a> <font color="Maroon" title="c9">t1</font>,<font color="Maroon" title="c2">S</font> )
 <b>by </b><i><a class="ref" href="rewrite2.html#D5" target="_self" title="REWRITE2:def.5">defDeriv1</a></i>;<br/>
<a NAME="E4:38"/>
<font color="Maroon" title="c8">s1</font> <a href="rewrite2.html#R1" title="REWRITE2:pred.1">--&gt;.</a> <font color="Maroon" title="c9">t1</font>,<font color="Maroon" title="c3">T</font>
 
<b>by </b><i><a class="txt" href="rewrite2.html#E1:38"><i><font color="Green" title="E20">A</font></i></a>, <a class="txt" href="rewrite2.html#E3:38"><i><font color="Green" title="E21">B</font></i></a>, <a class="ref" href="rewrite2.html#T18" target="_self" title="REWRITE2:th.18">ThProd90</a></i>;<br/>
<b>hence </b><a NAME="E5:38"/>
<font color="Maroon" title="c4">s</font> <a href="rewrite2.html#R2" title="REWRITE2:pred.2">==&gt;.</a> <font color="Maroon" title="c5">t</font>,<font color="Maroon" title="c3">T</font>
 <b>by </b><i><a class="txt" href="rewrite2.html#E3:38"><i><font color="Green" title="E21">B</font></i></a>, <a class="ref" href="rewrite2.html#D5" target="_self" title="REWRITE2:def.5">defDeriv1</a></i>;<br/>


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