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<b>let </b><font color="Maroon">c<sub>1</sub></font> be   <a href="nat_1.html#NM1">Nat</a>;<br/>

<a NAME="E1:47"/>
 <a href="heyting3.html#K2" target="_self">PFArt</a> 1,<font color="Maroon">c<sub>1</sub></font> <a href="hidden.html#R2">in</a>  <a href="heyting3.html#K4" target="_self">PFBrt</a> 1,<font color="Maroon">c<sub>1</sub></font>
 
<b>by </b><i><a class="ref" href="heyting3.html#D4" target="_self">Def4</a></i>;<br/>
<b>hence </b><a NAME="E2:47"/>
 <a href="heyting3.html#K4" target="_self">PFBrt</a> 1,<font color="Maroon">c<sub>1</sub></font> <a href="hidden.html#NR2" target="_self">&lt;&gt;</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>
 <b>by </b><i><a class="ref" href="tarski.html#D1">TARSKI:def 1</a></i>;<br/>


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