intros.
simpl in |- *; auto with algebra.
Qed.
Hint Resolve modify_tl_hd: algebra.

Lemma modify_tl_tl :
forall (A : Setoid) (n : Nat) (v : seq (S n) A) (m : Nat)
(HS : S m < S n) (H : m < n) (a : A),
Seqtl (modify_seq v (Build_finiteT HS) a) ='
modify_seq (Seqtl v) (Build_finiteT H) a in _.