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).

Lemma firstr_firstl :
forall x, firstr x = firstl (nshiftl x (pred size)).