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_lxor_spec p p' n : testbit (Pos.lxor p p') n = xorb (Pos.testbit p n) (Pos.testbit p' n).