(** * Properties of shifts *)
(** First, a unified specification for [shiftl] : the [shiftl_spec] below (combined with [testbit_neg_r]) is equivalent to [shiftl_spec_low] and [shiftl_spec_high]. *)

(** Shifts correspond to multiplication or division by a power of two *)
Lemma shiftr_div_pow2 : forall a n, 0<=n -> a >> n == a / 2^n.