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<b>defpred </b><font color="Maroon">S<sub>1</sub></font>[ <a href="ordinal1.html#V7">natural</a>  <a href="ordinal1.html#NM1" target="_self">number</a> ] <b>means </b><font color="Maroon">a<sub>1</sub></font> <a href="newton.html#K6" target="_self">!</a>  <a href="xxreal_0.html#NR4" target="_self">&gt;</a> 0;<br/>
<a NAME="E1:26"/><i><font color="Green">E41</font></i>: 
<font color="Maroon">S<sub>1</sub></font>[0]
 
<b>by </b><i/>;<br/>
<div><i><font color="Green">E42</font></i>: <a class="txt" onclick="hs2(this)" href="javascript:()" title="26_1"><b>now </b></a><div class="add"><b>let </b><font color="Maroon">s</font> be   <a href="nat_1.html#NM1">Nat</a>;<br/><b>assume </b><a NAME="E1:26_1"/>
<font color="Maroon">S<sub>1</sub></font>[<font color="Maroon">s</font>]
 ;<br/><a NAME="E2:26_1"/><b>then </b>
<span class="p1">(<span class="default"><font color="Maroon">s</font> <a href="xcmplx_0.html#K2">+</a> 1</span>)</span> <a href="xcmplx_0.html#K3">*</a> <span class="p1">(<span class="default"><font color="Maroon">s</font> <a href="newton.html#K6" target="_self">!</a> </span>)</span> <a href="xxreal_0.html#NR4" target="_self">&gt;</a> <span class="p1">(<span class="default"><font color="Maroon">s</font> <a href="xcmplx_0.html#K2">+</a> 1</span>)</span> <a href="xcmplx_0.html#K3">*</a> 0
 <b>by </b><i><a class="ref" href="xreal_1.html#T70">XREAL_1:70</a></i>;<br/><b>hence </b><a NAME="E3:26_1"/>
<font color="Maroon">S<sub>1</sub></font>[<font color="Maroon">s</font> <a href="xcmplx_0.html#K2">+</a> 1]
 <b>by </b><i/>;<br/></div><b>end;</b></div>
<b>thus </b><a NAME="E3:26"/>
for <font color="Olive">s</font> being  <a href="nat_1.html#NM1">Nat</a> holds  <font color="Maroon">S<sub>1</sub></font>[<font color="Olive">s</font>]
 <b>from </b><i><a class="ref" href="nat_1.html#S2">NAT_1:sch 2</a>(, );</i><br/>


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