(** Enumerating the bindings of a tree. *)
Parameter elements:
forall (A: Type), t A -> list (elt * A).

(* Specifications: *)
Axiom elements_correct:
forall (A: Type) (m: t A) (i: elt) (v: A),
get i m = Some v -> In (i, v) (elements m).
Axiom elements_complete:
forall (A: Type) (m: t A) (i: elt) (v: A),
In (i, v) (elements m) -> get i m = Some v.
Axiom elements_keys_norepet:
forall (A: Type) (m: t A),
list_norepet (List.map (@fst elt A) (elements m)).
Axiom elements_extensional:
forall (A: Type) (m n: t A),
(forall i, get i m = get i n) ->
elements m = elements n.
Axiom elements_remove:
forall (A: Type) i v (m: t A),
get i m = Some v ->
exists l1 l2, elements m = l1 ++ (i,v) :: l2 /\ elements (remove i m) = l1 ++ l2.