intros.
red in |- *.
intro.
generalize (le_or_lt n i).
intro p; inversion_clear p.
right; split; auto.
left.
repeat exists H0.
simpl in H; red in H; simpl in H; apply H.
Qed.
(** - And the other way around, if v and w happen to have the same type *)

Lemma seq_equal_map_equal :
forall (A : Setoid) (n : Nat) (v w : seq n A), seq_equal v w -> v =' w in _.