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<b>let </b><font color="Maroon">V</font> be   <a href="classes2.html#NM1">Universe</a>;<br/><b>let </b><font color="Maroon">X</font> be   <a href="zf_refle.html#NM1">Subclass</a> of <font color="Maroon">V</font>;<br/>



<b>assume </b><a NAME="E1:32"/><i><font color="Green">E56</font></i>: 
<font color="Maroon">X</font> is <a href="zf_fund1.html#V8" target="_self">closed_wrt_A1-A7</a>
 ;<br/>

<a NAME="E2:32"/><b>then </b><i><font color="Green">E57</font></i>: 
 <a href="xboole_0.html#K1">{}</a>  <a href="hidden.html#R2">in</a> <font color="Maroon">X</font>
 
<b>by </b><i/>;<br/>
<b>hence </b><a NAME="E3:32"/>
 <a href="ordinal4.html#K2">0-element_of</a> <font color="Maroon">V</font> <a href="hidden.html#R2">in</a> <font color="Maroon">X</font>
 <b>by </b><i><a class="ref" href="ordinal4.html#T35">ORDINAL4:35</a></i>;<br/>

<a NAME="E4:32"/><i><font color="Green">E61</font></i>: 
1 <a href="hidden.html#R1">=</a>  <a href="ordinal1.html#K1">succ</a> 0
 
;<br/>
<a NAME="E5:32"/>
<a href="xboole_0.html#K1">{}</a>  <a href="xboole_0.html#K2">\/</a> <span class="p1"><a href="tarski.html#K1">{</a><span class="default"><a href="xboole_0.html#K1">{}</a> </span><a href="tarski.html#K1">}</a></span> <a href="hidden.html#R2">in</a> <font color="Maroon">X</font>
 
<b>by </b><i>, , </i>;<br/>
<a NAME="E6:32"/><b>then </b>
1 <a href="hidden.html#R2">in</a> <font color="Maroon">X</font>
 
<b>by </b><i><a class="ref" href="ordinal1.html#D1">ORDINAL1:def 1</a>, </i>;<br/>
<b>hence </b><a NAME="E7:32"/>
 <a href="ordinal4.html#K3">1-element_of</a> <font color="Maroon">V</font> <a href="hidden.html#R2">in</a> <font color="Maroon">X</font>
 <b>by </b><i><a class="ref" href="ordinal4.html#T35">ORDINAL4:35</a></i>;<br/>


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