intros.
red in H.
case (H 0); clear H; intros.
inversion_clear H; inversion_clear H0.
apply Trans with (v (Build_finiteT x)); auto with algebra.
apply Trans with (w (Build_finiteT x0)); auto with algebra.
inversion_clear H; inversion_clear H0.
Qed.
Hint Resolve seq_equal_head: algebra.

Lemma seq_equal_seqtl :
forall (A : Setoid) (n m : Nat) (v : seq n A) (w : seq m A),
seq_equal v w -> seq_equal (Seqtl v) (Seqtl w).