Ltac simpl_of_lu :=
  match goal with
  | |- context [ of_lu (?f ?x) ] =>
    rewrite (of_lu_eqn (f x)); simpl hd; simpl tl
  end.

Lemma of_iff d d' : Nat.of_hex_uint d = Nat.of_hex_uint d' <-> unorm d = unorm d'.