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

<b>let </b><font color="Maroon">X</font> be    <a href="hidden.html#M1">set</a> ;<br/><b>let </b><font color="Maroon">A</font> be   <a href="ordinal1.html#NM2">Ordinal</a>;<br/>



<b>set </b><font color="Maroon">R</font> =  <a href="classes1.html#K6" target="_self">the_rank_of</a> <font color="Maroon">X</font>;<br/>
<a NAME="E1:77"/><i><font color="Green">E25</font></i>: 
( <font color="Maroon">X</font> <a href="tarski.html#R1">c=</a>  <a href="classes1.html#K4" target="_self">Rank</a> <span class="p1">(<span class="default"><a href="classes1.html#K6" target="_self">the_rank_of</a> <font color="Maroon">X</font></span>)</span> &amp; ( for <font color="Olive">B</font> being  <a href="ordinal1.html#NM2">Ordinal</a>  st <font color="Maroon">X</font> <a href="tarski.html#R1">c=</a>  <a href="classes1.html#K4" target="_self">Rank</a> <font color="Olive">B</font> holds <br/> <a href="classes1.html#K6" target="_self">the_rank_of</a> <font color="Maroon">X</font> <a href="ordinal1.html#R1">c=</a> <font color="Olive">B</font> ) )
 
<b>by </b><i/>;<br/>
<b>thus </b><a NAME="E2:77"/>
(  <a href="classes1.html#K6" target="_self">the_rank_of</a> <font color="Maroon">X</font> <a href="ordinal1.html#R1">c=</a> <font color="Maroon">A</font> implies for <font color="Olive">Y</font> being   <a href="hidden.html#M1">set</a>   st <font color="Olive">Y</font> <a href="hidden.html#R2">in</a> <font color="Maroon">X</font> holds <br/> <a href="classes1.html#K6" target="_self">the_rank_of</a> <font color="Olive">Y</font> <a href="hidden.html#R2">in</a> <font color="Maroon">A</font> )
 <div><a class="txt" onclick="hs2(this)" href="javascript:()" title="77_1"><b>proof </b></a><div class="add">

<b>assume </b><a NAME="E1:77_1"/><i><font color="Green">E26</font></i>: 
 <a href="classes1.html#K6" target="_self">the_rank_of</a> <font color="Maroon">X</font> <a href="ordinal1.html#R1">c=</a> <font color="Maroon">A</font>
 ;<br/>

<b>let </b><font color="Maroon">Y</font> be    <a href="hidden.html#M1">set</a> ;<br/>

<b>assume </b><a NAME="E2:77_1"/>
<font color="Maroon">Y</font> <a href="hidden.html#R2">in</a> <font color="Maroon">X</font>
 ;<br/>

<a NAME="E3:77_1"/><b>then </b>
( <font color="Maroon">Y</font> <a href="hidden.html#R2">in</a>  <a href="classes1.html#K4" target="_self">Rank</a> <span class="p1">(<span class="default"><a href="classes1.html#K6" target="_self">the_rank_of</a> <font color="Maroon">X</font></span>)</span> &amp;  <a href="classes1.html#K4" target="_self">Rank</a> <span class="p1">(<span class="default"><a href="classes1.html#K6" target="_self">the_rank_of</a> <font color="Maroon">X</font></span>)</span> <a href="tarski.html#R1">c=</a>  <a href="classes1.html#K4" target="_self">Rank</a> <font color="Maroon">A</font> )
 
<b>by </b><i>, , </i>;<br/>
<b>hence </b><a NAME="E4:77_1"/>
 <a href="classes1.html#K6" target="_self">the_rank_of</a> <font color="Maroon">Y</font> <a href="hidden.html#R2">in</a> <font color="Maroon">A</font>
 <b>by </b><i/>;<br/>


</div><b>end;</b></div>

<b>assume </b><a NAME="E3:77"/><i><font color="Green">E29</font></i>: 
for <font color="Olive">Y</font> being   <a href="hidden.html#M1">set</a>   st <font color="Olive">Y</font> <a href="hidden.html#R2">in</a> <font color="Maroon">X</font> holds <br/> <a href="classes1.html#K6" target="_self">the_rank_of</a> <font color="Olive">Y</font> <a href="hidden.html#R2">in</a> <font color="Maroon">A</font>
 ;<br/>

<a NAME="E4:77"/>
<font color="Maroon">X</font> <a href="tarski.html#R1">c=</a>  <a href="classes1.html#K4" target="_self">Rank</a> <font color="Maroon">A</font>
 
<div><a class="txt" onclick="hs2(this)" href="javascript:()" title="77_2"><b>proof </b></a><div class="add">

<b>let </b><font color="Maroon">x</font> be    <a href="hidden.html#M1">set</a> ; <i><font color="Red">:: according to </font></i><a class="ref" href="tarski.html#D3">TARSKI:def 3</a><br/>

<b>assume </b><a NAME="E1:77_2"/>
<font color="Maroon">x</font> <a href="hidden.html#R2">in</a> <font color="Maroon">X</font>
 ;<br/>

<a NAME="E2:77_2"/><b>then </b>
 <a href="classes1.html#K6" target="_self">the_rank_of</a> <font color="Maroon">x</font> <a href="hidden.html#R2">in</a> <font color="Maroon">A</font>
 
<b>by </b><i/>;<br/>
<b>hence </b><a NAME="E3:77_2"/>
<font color="Maroon">x</font> <a href="hidden.html#R2">in</a>  <a href="classes1.html#K4" target="_self">Rank</a> <font color="Maroon">A</font>
 <b>by </b><i/>;<br/>


</div><b>end;</b></div>
<b>hence </b><a NAME="E5:77"/>
 <a href="classes1.html#K6" target="_self">the_rank_of</a> <font color="Maroon">X</font> <a href="ordinal1.html#R1">c=</a> <font color="Maroon">A</font>
 <b>by </b><i/>;<br/>


</div>
