Ltac do_map_arg :=
match goal with |- ?a = ?b =>
match a with context [map ?x _] =>
match b with context [map ?y _] => replace y with x; auto end end end.

Lemma age1_resource_at:
forall phi phi',
age1 phi = Some phi' ->
forall loc r,
phi @ loc = resource_fmap (approx (level phi)) r ->
phi' @ loc = resource_fmap (approx (level phi')) r.