induction n1 as [|n1 IHn1]; simpl; intros n2 n3 Heq w; intuition.
rewrite (UIP_dec eq_nat_dec Heq (refl_equal _)); reflexivity.
rewrite (IHn1 _ _ (plus_assoc _ _ _)).
f_equal.
apply wtl_match.
Qed.

Lemma wtl_eq_rect_mul : forall n w b Heq Heq',
wtl (eq_rect (S n) word (WS b w) (S (n * 1)) Heq) =
eq_rect _ word w _ Heq'.