Definition Zdivide_dec:
forall (p q: Z), p > 0 -> { (p|q) } + { ~(p|q) }.
(** Conversion from [Z] to [nat]. *)
Definition nat_of_Z: Z -> nat := Z.to_nat.

(* Specifications: *)
Lemma nat_of_Z_of_nat:
forall n, nat_of_Z (Z.of_nat n) = n.
Lemma nat_of_Z_max:
forall z, Z.of_nat (nat_of_Z z) = Z.max z 0.
Lemma nat_of_Z_eq:
forall z, z >= 0 -> Z.of_nat (nat_of_Z z) = z.
Lemma nat_of_Z_neg:
forall n, n <= 0 -> nat_of_Z n = O.
Lemma nat_of_Z_plus:
forall p q,
p >= 0 -> q >= 0 ->
nat_of_Z (p + q) = (nat_of_Z p + nat_of_Z q)%nat.