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 uniq_app_iff :
uniq (E ++ F) <-> uniq E /\ uniq F /\ disjoint E F.