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

Lemma to_of_lu_tenfold d :
to_lu (of_lu d) = lnorm d ->
to_lu (10 * of_lu d) = lnorm (D0 d).