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<b>let </b><font color="Maroon">r</font> be  <a href="xreal_0.html#V1">real</a>  <a href="ordinal1.html#NM1" target="_self">number</a> ;<br/><b>let </b><font color="Maroon">k</font> be  <a href="ordinal1.html#V7">natural</a>  <a href="ordinal1.html#NM1" target="_self">number</a> ;<br/>



<a NAME="E1:7"/><i><font color="Green">E21</font></i>: 
<font color="Maroon">k</font> <a href="hidden.html#R2">in</a>  <a href="numbers.html#K5">NAT</a> 
 
<b>by </b><i><a class="ref" href="ordinal1.html#D13">ORDINAL1:def 13</a></i>;<br/>
<b>assume </b><a NAME="E2:7"/>
( <font color="Maroon">r</font> <a href="hidden.html#R1">=</a> <font color="Maroon">k</font> or <font color="Maroon">r</font> <a href="hidden.html#R1">=</a>  <a href="xcmplx_0.html#K4">-</a> <font color="Maroon">k</font> )
 ;<br/>

<a NAME="E3:7"/><b>then </b>
<font color="Maroon">r</font> <a href="hidden.html#R2">in</a>  <a href="numbers.html#K4">INT</a> 
 
<b>by </b><i>, </i>;<br/>
<b>hence </b><a NAME="E4:7"/>
<font color="Maroon">r</font> is   <a href="int_1.html#NM1">Integer</a>
 <b>by </b><i/>;<br/>


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