Ltac wlt_ind :=
  match goal with
  | [ |- forall (n: word ?len), ?P ] =>
    refine (well_founded_ind (@wlt_wf len) (fun n => P) _)
  end.

Theorem div2_pow2_twice: forall n, Nat.div2 (pow2 n + (pow2 n + 0)) = pow2 n.