Hint Resolve @pure_intersection1 @pure_intersection2.

(* Specifications: *)
Lemma FF_andp {A} `{ageable A}:  forall P: pred A, FF && P = FF.
Lemma andp_FF {A}`{ageable A}:  forall P: pred A, P && FF = FF.
Hint Rewrite @FF_andp @andp_FF : normalize.