Parameter eq_dec : forall x y : t, { eq x y } + { ~ eq x y }.
End UsualOrderedType.
(** a [UsualOrderedType] is in particular an [OrderedType]. *)
Module UOT_to_OT (U:UsualOrderedType) <: OrderedType := U.
(** [nat] is an ordered type with respect to the usual order on natural numbers. *)
Module Nat_as_OT <: UsualOrderedType.
Definition t := nat.
Definition eq := @eq nat.
Definition eq_refl := @eq_refl t.
Definition eq_sym := @eq_sym t.
Definition eq_trans := @eq_trans t.
Definition lt := lt.

Lemma eq_sym : forall x y : t, eq x y -> eq y x.