................
&gt; &gt; &gt; &gt;
&gt; &gt; &gt; &gt; Of course, I think what you *really* want is
&gt; &gt; &gt; &gt; the purely generalized form of this axiom,
&gt; &gt; &gt; &gt; of which the above is just an instance:
&gt; &gt; &gt; &gt;
&gt; &gt; &gt; &gt; (forall (?x ?y ?z)
&gt; &gt; &gt; &gt;         (&lt;=&gt; (gives ?x ?y ?z)
&gt; &gt; &gt; &gt;              (exists (?e)
&gt; &gt; &gt; &gt;                      (and (giving ?e)
&gt; &gt; &gt; &gt;                           (giver ?e ?x)
&gt; &gt