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 binds_app_uniq_iff :
uniq (E ++ F) ->
(binds x a (E ++ F) <->
(binds x a E /\ ~ In x (dom F)) \/
(binds x a F /\ ~ In x (dom E))).