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<b>let </b><font color="Maroon" title="c1">s</font> be   <a href="nat_1.html#NM1" title="NAT_1:NM.1">Nat</a>;<br/>

<b>defpred </b><font color="Maroon">S<sub>1</sub></font>[  <a href="nat_1.html#NM1" title="NAT_1:NM.1">Nat</a>] <b>means </b>$1 <a href="newton.html#K6" title="NEWTON:func.6">!</a>  is    <a href="subset_1.html#M2" title="SUBSET_1:mode.2">Element</a> of  <a href="numbers.html#K5" title="NUMBERS:func.5">NAT</a> ;<br/>
<a NAME="E1:25"/><i><font color="Green" title="E12">A1</font></i>: 
<font color="Maroon">S<sub>1</sub></font>[ <a href="numbers.html#K6" title="NUMBERS:func.6">0</a> ]
 
<b>by </b><i><a class="ref" href="finseq_2.html#T58" title="FINSEQ_2:th.58">FINSEQ_2:58</a>, <a class="ref" href="rvsum_1.html#T124" title="RVSUM_1:th.124">RVSUM_1:124</a></i>;<br/>
<div><i><font color="Green" title="E13">A2</font></i>: <a class="txt" onclick="hs2(this)" href="javascript:()" title="25_1"><b>now </b></a><div class="add"><b>let </b><font color="Maroon" title="c2">s</font> be   <a href="nat_1.html#NM1" title="NAT_1:NM.1">Nat</a>;<br/><b>assume </b><a NAME="E1:25_1"/>
<font color="Maroon">S<sub>1</sub></font>[<font color="Maroon" title="c2">s</font>]
 ;<br/><b>then reconsider </b><font color="Maroon" title="c3">k</font> = <font color="Maroon" title="c2">s</font> <a href="newton.html#K6" title="NEWTON:func.6">!</a>  as    <a href="subset_1.html#M2" title="SUBSET_1:mode.2">Element</a> of  <a href="numbers.html#K5" title="NUMBERS:func.5">NAT</a>  ;<br/><a NAME="E3:25_1"/>
<span class="p1">(<span class="default"><font color="Maroon" title="c2">s</font> <a href="nat_1.html#K1" title="NAT_1:func.1">+</a> 1</span>)</span> <a href="newton.html#K6" title="NEWTON:func.6">!</a>  <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a> <span class="p1">(<span class="default"><font color="Maroon" title="c2">s</font> <a href="nat_1.html#K1" title="NAT_1:func.1">+</a> 1</span>)</span> <a href="nat_1.html#K4" title="NAT_1:func.4">*</a> <font color="Maroon" title="c3">k</font>
 <b>by </b><i><a class="ref" href="newton.html#T21" target="_self" title="NEWTON:th.21">Th21</a></i>;<br/><b>hence </b><a NAME="E4:25_1"/>
<font color="Maroon">S<sub>1</sub></font>[<font color="Maroon" title="c2">s</font> <a href="nat_1.html#K1" title="NAT_1:func.1">+</a> 1]
 ;<br/></div><b>end;</b></div>
<a NAME="E3:25"/>
for <font color="Olive" title="b1">s</font> being  <a href="nat_1.html#NM1" title="NAT_1:NM.1">Nat</a> holds  <font color="Maroon">S<sub>1</sub></font>[<font color="Olive" title="b1">s</font>]
 
<b>from </b><i><a class="ref" href="nat_1.html#S2" title="NAT_1:sch.2">NAT_1:sch 2</a>(<a class="txt" href="newton.html#E1:25"><i><font color="Green" title="E12">A1</font></i></a>, <a class="txt" href="newton.html#E2:25"><i><font color="Green" title="E13">A2</font></i></a>);<br/></i>
<b>hence </b><a NAME="E4:25"/>
<font color="Maroon" title="c1">s</font> <a href="newton.html#K6" title="NEWTON:func.6">!</a>  is    <a href="subset_1.html#M2" title="SUBSET_1:mode.2">Element</a> of  <a href="numbers.html#K5" title="NUMBERS:func.5">NAT</a> 
 ;<br/>


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