Section EqShiftL.
(** After killing [n] bits at the left, are the numbers equal ?*)
Definition EqShiftL n x y :=
nshiftl x n = nshiftl y n.
(** * From int31 to list of digits. *)
(** Lower (=rightmost) bits comes first. *)
Definition i2l := recrbis _ nil (fun d _ rec => d::rec).

Lemma i2l_length : forall x, length (i2l x) = size.