(** * 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 inj_zexp : forall (n : nat) (a : Z), ZExp a (Z_of_nat n) = Exp a n.