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<b>let </b><font color="Maroon">A</font> be    <a href="hidden.html#M1">set</a> ;<br/><b>let </b><font color="Maroon">u</font> be   <a href="struct_0.html#NM1">Element</a> of <span class="p1">(<span class="default"><a href="normform.html#K12">NormForm</a> <font color="Maroon">A</font></span>)</span>;<br/><b>let </b><font color="Maroon">X</font> be    <a href="hidden.html#M1">set</a> ;<br/>





<a NAME="E1:11"/><i><font color="Green">E21</font></i>: 
<font color="Maroon">u</font> <a href="hidden.html#R1">=</a>  <a href="heyting1.html#K3" target="_self">@</a> <font color="Maroon">u</font>
 
;<br/>
<b>assume </b><a NAME="E2:11"/>
<font color="Maroon">X</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">u</font>
 ;<br/>

<a NAME="E3:11"/><b>then </b>
<font color="Maroon">X</font> <a href="hidden.html#R2">in</a>  <a href="normform.html#K8">Normal_forms_on</a> <font color="Maroon">A</font>
 
<b>by </b><i>, </i>;<br/>
<b>hence </b><a NAME="E4:11"/>
<font color="Maroon">X</font> is   <a href="struct_0.html#NM1">Element</a> of <span class="p1">(<span class="default"><a href="normform.html#K12">NormForm</a> <font color="Maroon">A</font></span>)</span>
 <b>by </b><i><a class="ref" href="normform.html#D14">NORMFORM:def 14</a></i>;<br/>


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