Module Make
(X : UsualDecidableType)
(KeySet : FSetInterface.WSfun X).
(* SCW: Make an instance of EqDef_eq for X so that we can use the "==" in [get] below. *)
Instance EqDec_of_X : @EqDec X.t eq eq_equivalence.

Lemma disjoint_app_r :
forall A B (E F : list (X.t*A)) (G : list (X.t*B)),
disjoint G (E ++ F) <-> disjoint E G /\ disjoint F G.