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))))