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<div><span class="kw">theorem </span><span class="lab"><font color="Green" title="E28">Th21</font></span>: <a NAME="T21"><span class="comment"><font color="firebrick">:: HEYTING1:21</font></span><br/></a><div class="add"> for <font color="Olive" title="b1">A</font> being    <a href="hidden.html#M2" title="HIDDEN:mode.2">set</a> <br/>  for <font color="Olive" title="b2">K</font> being    <a href="subset_1.html#M2" title="SUBSET_1:mode.2">Element</a> of  <a href="normform.html#K8" title="NORMFORM:func.8">Normal_forms_on</a> <font color="Olive" title="b1">A</font> holds  <font color="Olive" title="b2">K</font> <a href="normform.html#K10" title="NORMFORM:func.10">^</a> <span class="p1">(<span class="default"><a href="heyting1.html#K6" title="HEYTING1:func.6">-</a> <font color="Olive" title="b2">K</font></span>)</span> <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a>  <a href="xboole_0.html#K1" title="XBOOLE_0:func.1">{}</a> </div></div>
