 ) argument position, there is at most one legal occupant THING2 of PRED's second (or arg2 ) argument position such that (PRED THING1 THING2) holds. (The foregoing sufficient condition is not necessary in the case where the arg2 entry-format of PRED is #$intervalEntryFormatInArgs (q.v.) instead of #$singleEntryFormatInArgs; see the comment for #$FunctionalPredicate for that case. Cf. #$StrictlyFunctionalSlot.) #$FunctionalSlot is thus the subcollection of the collection-intersection of #$BinaryPredicate and