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

<a NAME="E1:23"/>
 <a href="xboole_0.html#K1">{}</a>  <a href="tarski.html#R1">c=</a> <font color="Maroon">X</font>
 
<b>by </b><i><a class="ref" href="xboole_1.html#T2">XBOOLE_1:2</a></i>;<br/>
<a NAME="E2:23"/><b>then </b>
(  <a href="card_1.html#K1" target="_self">Card</a> <a href="xboole_0.html#K1">{}</a>  <a href="card_1.html#NR1" target="_self">&lt;=`</a>  <a href="card_1.html#K1" target="_self">Card</a> <font color="Maroon">X</font> &amp;  <a href="card_1.html#K1" target="_self">Card</a> <font color="Maroon">X</font> <a href="card_1.html#NR2" target="_self">&lt;`</a>  <a href="card_1.html#K2" target="_self">nextcard</a> <font color="Maroon">X</font> )
 
<b>by </b><i>, </i>;<br/>
<b>hence </b><a NAME="E3:23"/>
 <a href="card_1.html#K1" target="_self">Card</a> <a href="xboole_0.html#K1">{}</a>  <a href="card_1.html#NR2" target="_self">&lt;`</a>  <a href="card_1.html#K2" target="_self">nextcard</a> <font color="Maroon">X</font>
 <b>by </b><i><a class="ref" href="ordinal1.html#T22">ORDINAL1:22</a></i>;<br/>


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