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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="trees_1.html#M1">Element</a> of <font color="Maroon">t</font>;<br/>



<a NAME="E1:13"/><i><font color="Green">E22</font></i>: 
not <span class="p1"><a href="finseq_1.html#K12">&lt;*</a><span class="default">0</span><a href="finseq_1.html#K12">*&gt;</a></span> <a href="hidden.html#R2">in</a>  <a href="trees_1.html#K2">elementary_tree</a> 0
 
<b>by </b><i><a class="ref" href="tarski.html#D1">TARSKI:def 1</a>, <a class="ref" href="trees_1.html#T56">TREES_1:56</a></i>;<br/>
<div><b>hereby </b>
<div class="add"><b>assume </b><a NAME="E1:13_1"/>
<font color="Maroon">t</font> <a href="trees_1.html#K4">|</a> <font color="Maroon">p</font> <a href="hidden.html#R1">=</a>  <a href="trees_1.html#K2">elementary_tree</a> 0
 ;<br/><a NAME="E2:13_1"/><b>then </b>
not <font color="Maroon">p</font> <a href="finseq_1.html#K8">^</a> <span class="p1"><a href="finseq_1.html#K12">&lt;*</a><span class="default">0</span><a href="finseq_1.html#K12">*&gt;</a></span> <a href="hidden.html#R2">in</a> <font color="Maroon">t</font>
 <b>by </b><i>, <a class="ref" href="trees_1.html#D9">TREES_1:def 9</a></i>;<br/><b>hence </b><a NAME="E3:13_1"/>
<font color="Maroon">p</font> <a href="hidden.html#R2">in</a>  <a href="trees_1.html#K3">Leaves</a> <font color="Maroon">t</font>
 <b>by </b><i><a class="ref" href="modal_1.html#T53">MODAL_1:53</a></i>;<br/></div>
<b>end;</b></div>

<b>assume </b><a NAME="E3:13"/><i><font color="Green">E25</font></i>: 
<font color="Maroon">p</font> <a href="hidden.html#R2">in</a>  <a href="trees_1.html#K3">Leaves</a> <font color="Maroon">t</font>
 ;<br/>

<b>let </b><font color="Maroon">q</font> be    <a href="finseq_1.html#M2">FinSequence</a> of  <a href="numbers.html#K5">NAT</a> ; <i><font color="Red">:: according to </font></i><a class="ref" href="trees_2.html#D1">TREES_2:def 1</a><br/>

<div><b>hereby </b>
<div class="add"><b>assume </b><a NAME="E1:13_2"/>
<font color="Maroon">q</font> <a href="hidden.html#R2">in</a> <font color="Maroon">t</font> <a href="trees_1.html#K4">|</a> <font color="Maroon">p</font>
 ;<br/><a NAME="E2:13_2"/><b>then </b>
<font color="Maroon">p</font> <a href="finseq_1.html#K8">^</a> <font color="Maroon">q</font> <a href="hidden.html#R2">in</a> <font color="Maroon">t</font>
 <b>by </b><i><a class="ref" href="trees_1.html#D9">TREES_1:def 9</a></i>;<br/><a NAME="E3:13_2"/><b>then </b>
( not <font color="Maroon">p</font> <a href="trees_1.html#NR3" target="_self">is_a_proper_prefix_of</a> <font color="Maroon">p</font> <a href="finseq_1.html#K8">^</a> <font color="Maroon">q</font> &amp; <font color="Maroon">p</font> <a href="tarski.html#R1">is_a_prefix_of</a> <font color="Maroon">p</font> <a href="finseq_1.html#K8">^</a> <font color="Maroon">q</font> )
 <b>by </b><i>, <a class="ref" href="trees_1.html#T8">TREES_1:8</a>, <a class="ref" href="trees_1.html#D8">TREES_1:def 8</a></i>;<br/><b>then </b><font color="Maroon">p</font> <a href="finseq_1.html#K8">^</a> <font color="Maroon">q</font> = 
<font color="Maroon">p</font>
<b>by </b><i><a class="ref" href="xboole_0.html#D8">XBOOLE_0:def 8</a></i>
<br/>.= 
<font color="Maroon">p</font> <a href="finseq_1.html#K7">^</a> <a href="xboole_0.html#K1">{}</a> 
<b>by </b><i><a class="ref" href="finseq_1.html#T47">FINSEQ_1:47</a></i>
;<br/><a NAME="E5:13_2"/><b>then </b>
<font color="Maroon">q</font> <a href="hidden.html#R1">=</a>  <a href="xboole_0.html#K1">{}</a> 
 <b>by </b><i><a class="ref" href="finseq_1.html#T46">FINSEQ_1:46</a></i>;<br/><b>hence </b><a NAME="E6:13_2"/>
<font color="Maroon">q</font> <a href="hidden.html#R2">in</a>  <a href="trees_1.html#K2">elementary_tree</a> 0
 <b>by </b><i><a class="ref" href="trees_1.html#T47">TREES_1:47</a></i>;<br/></div>
<b>end;</b></div>

<b>assume </b><a NAME="E5:13"/>
<font color="Maroon">q</font> <a href="hidden.html#R2">in</a>  <a href="trees_1.html#K2">elementary_tree</a> 0
 ;<br/>

<a NAME="E6:13"/><b>then </b>
<font color="Maroon">q</font> <a href="hidden.html#R1">=</a>  <a href="xboole_0.html#K1">{}</a> 
 
<b>by </b><i><a class="ref" href="tarski.html#D1">TARSKI:def 1</a>, <a class="ref" href="trees_1.html#T56">TREES_1:56</a></i>;<br/>
<b>hence </b><a NAME="E7:13"/>
<font color="Maroon">q</font> <a href="hidden.html#R2">in</a> <font color="Maroon">t</font> <a href="trees_1.html#K4">|</a> <font color="Maroon">p</font>
 <b>by </b><i><a class="ref" href="trees_1.html#T47">TREES_1:47</a></i>;<br/>


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