intros n x y X Y l.
apply comparisonL.
unfold ValB in |- *.
unfold Cons in |- *.
unfold Digit in |- *.
apply comp_dif.
auto.
Qed.
Hint Resolve Comp_dif.

(* Specifications: *)
Lemma Comp_eq :
forall (n : nat) (x y : Digit) (X Y : Num n),
valB x = valB y ->
Compare_Nat.comparison (ValB (S n) (Cons n x X)) (ValB (S n) (Cons n y Y)) =
Compare_Nat.comparison (ValB n X) (ValB n Y).