intros.
simpl in |- *.
apply Ap_comp; auto with algebra.
Qed.
Hint Resolve Seqtl_to_seq: algebra.

Lemma split_hd_tl_equality :
forall v w : seq (S n) A,
head v =' head w in _ -> Seqtl v =' Seqtl w in _ -> v =' w in _.