A simple set is a set that can be a member of another set.
(<=> (Simple-Set ?X) (And (Set ?X) (Bounded ?X)))
(Bounded ?X) (Set ?X)
(<=> (Simple-Set ?X) (And (Set ?X) (Bounded ?X)))
(=> (Setof $X $Y) (Simple-Set $Y))
(=> (= (Generalized-Union ?Set-Of-Sets) ?Set)
(Forall (?S) (=> (Member ?S ?Set-Of-Sets) (Simple-Set ?S))))
(=> (= (Generalized-Intersection ?Set-Of-Sets) ?Set)
(Forall (?S) (=> (Member ?S ?Set-Of-Sets) (Simple-Set ?S))))