destruct n.
intros; inversion_clear Heq.
intros.
apply Trans with (head v;; omit (Seqtl v) (Build_finiteT H));
auto with algebra.
Qed.
Hint Resolve omit_tlelt': algebra.

Lemma omit_tlelt'' :
forall (n : Nat) (A : Setoid) (v : seq (S n) A) (m : Nat)
(HS : S m < S n) (H : m < n) (Heq : S (pred n) = n),
seq_equal (omit v (Build_finiteT HS))
(head v;; omit (Seqtl v) (Build_finiteT H)).