(** The unary predicate [uniq] holds when each atom is bound at most once in an environment. *)

(* Specifications: *)
Lemma uniq_demo : forall (x y : atom) (T : typ),
x <> y -> uniq ((x ~ T) ++ (y ~ T)).
Lemma uniq_demo : forall (x y : atom) (T : typ),
x <> y -> uniq ((x ~ T) ++ (y ~ T)).