<?xml version="1.0"?>
<div class="add">

<b>let </b><font color="Maroon">W</font> be   <a href="trees_1.html#NM1">Tree</a>;<br/>

<b>reconsider </b><font color="Maroon">S</font> =  <a href="xboole_0.html#K1">{}</a>  as   <a href="subset_1.html#NM2">Subset</a> of <font color="Maroon">W</font> <b>by </b><i><a class="ref" href="xboole_1.html#T2">XBOOLE_1:2</a></i>;<br/>
<a NAME="E2:28"/>
<font color="Maroon">S</font> is    <a href="trees_2.html#M1" target="_self">Chain</a> of <font color="Maroon">W</font>
 
<div><a class="txt" onclick="hs2(this)" href="javascript:()" title="28_1"><b>proof </b></a><div class="add">

<b>let </b><font color="Maroon">p</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#D3" target="_self">TREES_2:def 3</a><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> ;<br/>



<b>thus </b><a NAME="E1:28_1"/>
( <font color="Maroon">p</font> <a href="hidden.html#R2">in</a> <font color="Maroon">S</font> &amp; <font color="Maroon">q</font> <a href="hidden.html#R2">in</a> <font color="Maroon">S</font> implies <font color="Maroon">p</font>,<font color="Maroon">q</font> <a href="xboole_0.html#R3">are_c=-comparable</a>  )
 ;<br/>


</div><b>end;</b></div>
<b>hence </b><a NAME="E3:28"/>
 <a href="xboole_0.html#K1">{}</a>  is    <a href="trees_2.html#M1" target="_self">Chain</a> of <font color="Maroon">W</font>
 ;<br/>


</div>
