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<b>let </b><font color="Maroon">c<sub>1</sub></font> be   <a href="nat_1.html#NM1">Nat</a>;<br/>

<b>assume </b><a NAME="E1:27"/><i><font color="Green">E28</font></i>: 
( 1 <a href="xxreal_0.html#R1">&lt;</a> <font color="Maroon">c<sub>1</sub></font> &amp; <font color="Maroon">c<sub>1</sub></font> <a href="xxreal_0.html#R1">&lt;</a> 5 &amp; <font color="Maroon">c<sub>1</sub></font> is <a href="int_2.html#V1">prime</a> )
 ;<br/>

<a NAME="E2:27"/><b>then </b>
( 1 <a href="binop_2.html#K23">+</a> 1 <a href="xxreal_0.html#R1">&lt;</a> <font color="Maroon">c<sub>1</sub></font> <a href="binop_2.html#K23">+</a> 1 &amp; <font color="Maroon">c<sub>1</sub></font> <a href="xxreal_0.html#R1">&lt;</a> 4 <a href="binop_2.html#K23">+</a> 1 )
 
<b>by </b><i><a class="ref" href="xreal_1.html#T8">XREAL_1:8</a></i>;<br/>
<a NAME="E3:27"/><b>then </b>
( ( 2 <a href="xxreal_0.html#R1">&lt;=</a> <font color="Maroon">c<sub>1</sub></font> &amp; <font color="Maroon">c<sub>1</sub></font> <a href="xxreal_0.html#R1">&lt;=</a> 2 <a href="binop_2.html#K23">+</a> 1 ) or ( 3 <a href="xxreal_0.html#R1">&lt;=</a> <font color="Maroon">c<sub>1</sub></font> &amp; <font color="Maroon">c<sub>1</sub></font> <a href="xxreal_0.html#R1">&lt;=</a> 3 <a href="binop_2.html#K23">+</a> 1 ) )
 
<b>by </b><i><a class="ref" href="nat_1.html#T38">NAT_1:38</a></i>;<br/>
<b>hence </b><a NAME="E4:27"/>
( <font color="Maroon">c<sub>1</sub></font> <a href="hidden.html#R1">=</a> 2 or <font color="Maroon">c<sub>1</sub></font> <a href="hidden.html#R1">=</a> 3 )
 <b>by </b><i><a class="txt" href="nat_4.html#E1:27"><i><font color="Green">E28</font></i></a>, <a class="ref" href="int_2.html#T46">INT_2:46</a>, <a class="ref" href="nat_1.html#T27">NAT_1:27</a></i>;<br/>


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