Entity ?x))
&gt; &gt;
&gt; &gt; (documentation "AXIOM: Everything is either a class or an entity, but 
&gt; not both.")
&gt; &gt;
&gt; &gt; (forall (?x)
&gt; &gt;         (and (or (Class ?x)
&gt; &gt;                  (Entity ?x))
&gt; &gt;              (&lt;=&gt; (Entity ?x)
&gt; &gt;                   (not (Class ?x)))))
&gt; &gt;
&gt; &gt; (documentation "AXIOM: Only entities are instances of classes, and only 
&gt; classes have instances.")
&gt; &gt;
&gt; &gt; (forall (?x)
&gt; &gt;         (=&gt; (inst