(** Low and high bounds for a given type. *)
Parameter high_bound: t -> t.

(* Specifications: *)
Axiom low_bound_sub: forall t, sub (low_bound t) t.
Axiom low_bound_minorant: forall x y, sub x y -> sub (low_bound y) x.
Axiom high_bound_sub: forall t, sub t (high_bound t).
Axiom high_bound_majorant: forall x y, sub x y -> sub y (high_bound x).
Parameter weight: t -> nat.