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<b>let </b><font color="Maroon">c<sub>20</sub></font> be    <a href="subset_1.html#M1">Element</a> of <font color="Maroon">c<sub>4</sub></font>;<br/>

<a NAME="E1:23"/>
( <font color="Maroon">c<sub>20</sub></font> <a href="hidden.html#R1">=</a> <font color="Maroon">c<sub>1</sub></font> or <font color="Maroon">c<sub>20</sub></font> <a href="hidden.html#R1">=</a> <font color="Maroon">c<sub>2</sub></font> )
 
<b>by </b><i><a class="ref" href="tarski.html#D2">TARSKI:def 2</a></i>;<br/>
<b>hence </b><a NAME="E2:23"/>
( <font color="Maroon">c<sub>18</sub></font> <a href="binop_1.html#K2">.</a> <font color="Maroon">c<sub>20</sub></font>,<font color="Maroon">c<sub>5</sub></font> <a href="hidden.html#R1">=</a> <font color="Maroon">c<sub>20</sub></font> &amp; <font color="Maroon">c<sub>18</sub></font> <a href="binop_1.html#K2">.</a> <font color="Maroon">c<sub>5</sub></font>,<font color="Maroon">c<sub>20</sub></font> <a href="hidden.html#R1">=</a> <font color="Maroon">c<sub>20</sub></font> )
 <b>by </b><i><a class="txt" href="realset2.html#E25"><i><font color="Green">Lemma16</font></i></a>, <a class="txt" href="realset2.html#E26"><i><font color="Green">Lemma17</font></i></a>, <a class="txt" href="realset2.html#E28"><i><font color="Green">Lemma19</font></i></a>, <a class="txt" href="realset2.html#E29"><i><font color="Green">Lemma20</font></i></a>, <a class="txt" href="realset2.html#E31"><i><font color="Green">Lemma22</font></i></a>, <a class="txt" href="realset2.html#E32"><i><font color="Green">Lemma23</font></i></a>, <a class="ref" href="funct_1.html#D4">FUNCT_1:def 4</a></i>;<br/>


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