apply digitInv; auto.
rewrite pGivesBound.
rewrite Zabs_eq; auto with zarith.
rewrite Zabs_eq; auto with zarith.
rewrite pGivesBound; auto with zarith.
Qed.

(* Specifications: *)
Theorem vNumPrecision :
forall n : Z,
digit radix n <= precision -> (Zabs n < Zpos (vNum b))%Z.