Section Basics.
(** * Basic results about [iszero], [shiftl], [shiftr] *)
(** * Iterated shift to the right *)
Definition nshiftr x := nat_rect _ x (fun _ => shiftr).
(** * Iterated shift to the left *)
Definition nshiftl x := nat_rect _ x (fun _ => shiftl).
(** More advanced results about [nshiftr] *)

Lemma nshiftr_0_firstl : forall n x, n < size ->
nshiftr x n = 0 -> firstl x = D0.