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<b>let </b><font color="Maroon">c<sub>2</sub></font>, <font color="Maroon">c<sub>3</sub></font>, <font color="Maroon">c<sub>4</sub></font> be   <a href="card_1.html#NM1">Cardinal</a>;<br/>





<b>assume </b><a NAME="E1:78"/><i><font color="Green">E53</font></i>: 
( <font color="Maroon">c<sub>2</sub></font> <a href="card_2.html#K2">*`</a> <font color="Maroon">c<sub>3</sub></font> <a href="card_1.html#NR2" target="_self">&lt;`</a> <font color="Maroon">c<sub>2</sub></font> <a href="card_2.html#K2">*`</a> <font color="Maroon">c<sub>4</sub></font> &amp; not <font color="Maroon">c<sub>3</sub></font> <a href="card_1.html#NR2" target="_self">&lt;`</a> <font color="Maroon">c<sub>4</sub></font> )
 ;<br/>

<a NAME="E2:78"/><b>then </b>
( <font color="Maroon">c<sub>4</sub></font> <a href="card_1.html#NR1" target="_self">&lt;=`</a> <font color="Maroon">c<sub>3</sub></font> &amp; <font color="Maroon">c<sub>2</sub></font> <a href="card_1.html#NR1" target="_self">&lt;=`</a> <font color="Maroon">c<sub>2</sub></font> )
 
<b>by </b><i><a class="ref" href="card_1.html#T14">CARD_1:14</a></i>;<br/>
<a NAME="E3:78"/><b>then </b>
<font color="Maroon">c<sub>2</sub></font> <a href="card_2.html#K2">*`</a> <font color="Maroon">c<sub>4</sub></font> <a href="card_1.html#NR1" target="_self">&lt;=`</a> <font color="Maroon">c<sub>2</sub></font> <a href="card_2.html#K2">*`</a> <font color="Maroon">c<sub>3</sub></font>
 
<b>by </b><i><a class="ref" href="card_4.html#T68" target="_self">Th68</a></i>;<br/>
<b>hence </b><a NAME="E4:78"/>
contradiction
 <b>by </b><i><a class="txt" href="card_4.html#E1:78"><i><font color="Green">E53</font></i></a>, <a class="ref" href="card_1.html#T14">CARD_1:14</a></i>;<br/>


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