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<b>let </b><font color="Maroon">c<sub>1</sub></font> be    <a href="hidden.html#M1">set</a> ;<br/>

<b>assume </b><a NAME="E1:3_1_1"/>
<font color="Maroon">c<sub>1</sub></font> is <a href="margrel1.html#V2">boolean</a>
 ;<br/>

<a NAME="E2:3_1_1"/><b>then </b>
<font color="Maroon">c<sub>1</sub></font> <a href="hidden.html#R2">in</a>  <a href="margrel1.html#K6">BOOLEAN</a> 
 
<b>by </b><i><a class="ref" href="margrel1.html#D15">MARGREL1:def 15</a></i>;<br/>
<b>hence </b><a NAME="E3:3_1_1"/>
<font color="Maroon">c<sub>1</sub></font> is <a href="ordinal1.html#V7">natural</a>
 <b>by </b><i><a class="ref" href="margrel1.html#D12">MARGREL1:def 12</a>, <a class="ref" href="tarski.html#D2">TARSKI:def 2</a></i>;<br/>


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