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_lu_revapp d d' : of_lu (revapp d d') = of_lu (rev d) + of_lu d' * 10^usize d.