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_inj d d' :
Nat.of_hex_uint d = Nat.of_hex_uint d' -> unorm d = unorm d'.