Section NAT_AGEABLE.
Definition natLevel (x:nat) : nat := x.
Definition natAge1 (x:nat) : option nat :=
match x with
| 0 => None
| S n => Some n
end.
Definition natUnage (x:nat) : nat := S x.

(* Specifications: *)
Lemma ag_nat_facts :
ageable_facts nat natLevel natAge1.