(** * 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]. *)

Lemma shiftl_div_pow2 : forall a n, n<=0 -> a << n == a / 2^(-n).
#[global]
Instance shiftr_wd : Proper (eq==>eq==>eq) shiftr.