Instance agB : ageable B := (ag_bij _ _ ag bijAB).

Lemma age_core_eq {A}{JA: Join A}{PA: Perm_alg A}{SA: Sep_alg A}{agA: ageable A}{AgeA: Age_alg A}: forall x y x' y', age x x' -> age y y' -> core x = core y -> core x' = core y'.