Proof with auto.
induction v...
simpl.
rewrite IHv.
rewrite (e h)...
Qed. (* todo: as a morphism *)

(* vnth *)
Lemma natBelow0_rect: natBelow 0 -> forall T, T.
Definition natBelow_S_bla (T: Type) (n: nat) (b: natBelow n): T -> (natBelow (pred n) -> T) -> T :=
match b with
| mkNatBelow 0 _ => fun z s => z
| mkNatBelow (S i) p => fun z s => s (mkNatBelow i p)
end.