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<b>let </b><font color="Maroon">T</font> be   <a href="trees_1.html#NM1">Tree</a>;<br/><b>let </b><font color="Maroon">p</font> be   <a href="finseq_1.html#NM1">FinSequence</a>, <font color="Maroon">q</font> be   <a href="finseq_1.html#NM1">FinSequence</a>;<br/>



<b>assume </b><a NAME="E1:34"/><i><font color="Green">E28</font></i>: 
( <font color="Maroon">p</font> <a href="hidden.html#R2">in</a> <font color="Maroon">T</font> &amp; <font color="Maroon">q</font> <a href="tarski.html#R1">is_a_prefix_of</a> <font color="Maroon">p</font> )
 ;<br/>

<b>then reconsider </b><font color="Maroon">r</font> = <font color="Maroon">p</font> as    <a href="trees_1.html#M1" target="_self">Element</a> of <font color="Maroon">T</font> ;<br/>
<a NAME="E3:34"/><i><font color="Green">E29</font></i>: 
(  <a href="trees_1.html#K1" target="_self">ProperPrefixes</a> <font color="Maroon">r</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">T</font> &amp; ( <font color="Maroon">q</font> <a href="trees_1.html#NR3" target="_self">is_a_proper_prefix_of</a> <font color="Maroon">p</font> or <font color="Maroon">q</font> <a href="hidden.html#R1">=</a> <font color="Maroon">p</font> ) )
 
<b>by </b><i>, , <a class="ref" href="xboole_0.html#D8">XBOOLE_0:def 8</a></i>;<br/>
<a NAME="E4:34"/><b>then </b>
( <font color="Maroon">q</font> <a href="hidden.html#R2">in</a>  <a href="trees_1.html#K1" target="_self">ProperPrefixes</a> <font color="Maroon">p</font> or <font color="Maroon">p</font> <a href="hidden.html#R1">=</a> <font color="Maroon">q</font> )
 
<b>by </b><i/>;<br/>
<b>hence </b><a NAME="E5:34"/>
<font color="Maroon">q</font> <a href="hidden.html#R2">in</a> <font color="Maroon">T</font>
 <b>by </b><i/>;<br/>


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