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

<b>let </b><font color="Maroon">X</font> be  <a href="membered.html#V3" target="_self">rational-membered</a>  <a href="hidden.html#M1">set</a> ;<br/>

<b>assume </b><a NAME="E1:24"/><i><font color="Green">E18</font></i>: 
for <font color="Olive">w</font> being <a href="rat_1.html#V1">rational</a>  <a href="ordinal1.html#NM1" target="_self">number</a>  holds  <font color="Olive">w</font> <a href="hidden.html#R2">in</a> <font color="Maroon">X</font>
 ;<br/>

<b>thus </b><a NAME="E2:24"/>
<font color="Maroon">X</font> <a href="tarski.html#R1">c=</a>  <a href="numbers.html#K3">RAT</a> 
 <b>by </b><i><a class="txt" href="membered.html#E1"><i><font color="Green">Lemma9</font></i></a></i>; <i><font color="Red">:: according to </font></i><a class="ref" href="xboole_0.html#D10">XBOOLE_0:def 10</a><br/>

<b>let </b><font color="Maroon">e</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="E3:24"/>
<font color="Maroon">e</font> <a href="hidden.html#R2">in</a>  <a href="numbers.html#K3">RAT</a> 
 ;<br/>

<a NAME="E4:24"/><b>then </b>
<font color="Maroon">e</font> is <a href="rat_1.html#V1">rational</a>
 
<b>by </b><i><a class="ref" href="rat_1.html#D2">RAT_1:def 2</a></i>;<br/>
<b>hence </b><a NAME="E5:24"/>
<font color="Maroon">e</font> <a href="hidden.html#R2">in</a> <font color="Maroon">X</font>
 <b>by </b><i/>;<br/>


</div>
