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<span class="kw">let </span><font color="Maroon" title="c1">x</font> be    <a href="ordinal1.html#NM1" title="ORDINAL1:NM.1">number</a> ; <a class="txt" onclick="hs(this)" href="javascript:()"><span class="comment"><font color="firebrick">::  thesis: </font></span></a><span class="hide"> ( <font color="Maroon" title="c1">x</font> is  <a href="xboolean.html#V1" title="XBOOLEAN:attr.1">boolean</a>  implies <font color="Maroon" title="c1">x</font> is  <a href="ordinal1.html#V7" title="ORDINAL1:attr.7">natural</a>  )</span><br/>

<span class="kw">assume </span><a NAME="E1:3_4_1"/>
( <font color="Maroon" title="c1">x</font> <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a>  <a href="xboolean.html#K1" title="XBOOLEAN:func.1">FALSE</a>  or <font color="Maroon" title="c1">x</font> <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a>  <a href="xboolean.html#K2" title="XBOOLEAN:func.2">TRUE</a>  )
 ; <span class="comment"><font color="firebrick">:: according to </font></span><a class="ref" href="xboolean.html#D3" target="_self" title="XBOOLEAN:def.3">XBOOLEAN:def 3</a> <a class="txt" onclick="hs(this)" href="javascript:()"><span class="comment"><font color="firebrick">::  thesis: </font></span></a><span class="hide"> <font color="Maroon" title="c1">x</font> is  <a href="ordinal1.html#V7" title="ORDINAL1:attr.7">natural</a> </span><br/>

<span class="kw">hence </span><a NAME="E2:3_4_1"/>
<font color="Maroon" title="c1">x</font> is  <a href="ordinal1.html#V7" title="ORDINAL1:attr.7">natural</a> 
 ; <a class="txt" onclick="hs(this)" href="javascript:()"><span class="comment"><font color="firebrick">::  thesis: </font></span></a><span class="hide"> verum</span><br/>


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