Definition recursion {A} : A -> (N -> A -> A) -> N -> A :=
  peano_rect (fun _ => A).#[global]
Instance recursion_wd {A} (Aeq : relation A) :
 Proper (Aeq==>(Logic.eq==>Aeq==>Aeq)==>Logic.eq==>Aeq) recursion.

Lemma pos_pred_shiftl_high : forall p n m, n<=m -> testbit (Pos.pred_N (Pos.shiftl p n)) m = testbit (shiftl (Pos.pred_N p) n) m.