(** * Exponential function with exponent in Z. *)

Definition ZExp (a n : Z) : Z :=
  match n with
  | Z0 => 1%Z
  | Zpos p => Exp a (nat_of_P p)
  | Zneg p => Exp a (nat_of_P p)
  end.

Lemma zexp_pred_succ : forall a x : Z, ZExp a (x + 1 - 1) = ZExp a x.