(** Exotic operations *)
(** Axioms on operations which are just short cut *)

(* Specifications: *)
Axiom compare_def_spec : forall x y, compare x y = compare_def x y.
Axiom head0_spec : forall x, 0 < to_Z x ->
Z.div wB 2 <= 2 ^ (to_Z (head0 x)) * to_Z x < wB.
Axiom tail0_spec : forall x, 0 < to_Z x ->
exists y, Z0 <= y /\ to_Z x = (2 * y + 1) * (2 ^ to_Z (tail0 x)).