let check s nodes =
Debug.unsafe s;
TimeFix.start ();
let r = hard_fixpoint s nodes in
(* match easy_fixpoint s nodes with *)
(* | None -> *)
(* (match medium_fixpoint s nodes with *)
(* | None -> hard_fixpoint s nodes *)
(* | r -> r) *)
(* | r -> r *)
(* in *)
TimeFix.pause ();
r