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<a NAME="E1:6_1"/><i><font color="Green">E4</font></i>: 
<font color="Maroon">P<sub>1</sub></font>[0]
 
<b>by </b><i><a class="txt" href="nat_1.html#E1:6"><i><font color="Green">E2</font></i></a></i>;<br/>
<a NAME="E2:6_1"/><i><font color="Green">E5</font></i>: 
for <font color="Olive">b<sub>1</sub></font> being  <a href="nat_1.html#NM1">Nat</a> st <font color="Maroon">P<sub>1</sub></font>[<font color="Olive">b<sub>1</sub></font>] holds <br/><font color="Maroon">P<sub>1</sub></font>[<font color="Olive">b<sub>1</sub></font> <a href="nat_1.html#K1" target="_self">+</a> 1]
 
<b>by </b><i><a class="txt" href="nat_1.html#E2:6"><i><font color="Green">E3</font></i></a></i>;<br/>
<a NAME="E3:6_1"/><i><font color="Green">E6</font></i>: 
for <font color="Olive">b<sub>1</sub></font> being  <a href="nat_1.html#NM1">Nat</a> holds <font color="Maroon">P<sub>1</sub></font>[<font color="Olive">b<sub>1</sub></font>]
 
<b>from </b><i><a class="ref" href="nat_1.html#S1" target="_self">NAT_1:sch 1</a>(<a class="txt" href="nat_1.html#E1:6_1"><i><font color="Green">E4</font></i></a>, <a class="txt" href="nat_1.html#E2:6_1"><i><font color="Green">E5</font></i></a>);<br/></i>
<b>let </b><font color="Maroon">c<sub>1</sub></font> be  <a href="ordinal1.html#V7">natural</a>  <a href="ordinal1.html#NM1" target="_self">number</a> ;<br/>

<a NAME="E4:6_1"/>
<font color="Maroon">c<sub>1</sub></font> is   <a href="nat_1.html#NM1">Nat</a>
 
<b>by </b><i><a class="ref" href="ordinal1.html#D13">ORDINAL1:def 13</a></i>;<br/>
<b>hence </b><a NAME="E5:6_1"/>
<font color="Maroon">P<sub>1</sub></font>[<font color="Maroon">c<sub>1</sub></font>]
 <b>by </b><i><a class="txt" href="nat_1.html#E3:6_1"><i><font color="Green">E6</font></i></a></i>;<br/>


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