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<b>let </b><font color="Maroon">x</font> be    <a href="ordinal1.html#NM1" target="_self">number</a> ;<br/>

<b>assume </b><a NAME="E1:3_4_1"/>
( <font color="Maroon">x</font> <a href="hidden.html#R1">=</a>  <a href="xboolean.html#K1" target="_self">FALSE</a>  or <font color="Maroon">x</font> <a href="hidden.html#R1">=</a>  <a href="xboolean.html#K2" target="_self">TRUE</a>  )
 ; <i><font color="Red">:: according to </font></i><a class="ref" href="xboolean.html#D3" target="_self">XBOOLEAN:def 3</a><br/>

<b>hence </b><a NAME="E2:3_4_1"/>
<font color="Maroon">x</font> is <a href="ordinal1.html#V7">natural</a>
 ;<br/>


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