End NAT_AGEABLE.

(* Specifications: *)
Lemma laterR_level' {A} `{H : ageable A}: forall {w1 w2: A}, laterR w1 w2 -> @laterR _ ag_nat (level w1) (level w2).
Lemma necR_nat {A} `{H : ageable A}:
forall {x y: A}, necR x y -> @necR nat ag_nat (level x) (level y).