Local Open Scope pred.
Section extensions.
Context {CS: compspecs} {Espec: OracleKind}.
(* Scall *)

Lemma later_twin {A} `{ageable A}:
forall phi1 phi2 phi1',
level phi1 = level phi2 ->
laterR phi1 phi1' ->
exists phi2', level phi1' = level phi2' /\ laterR phi2 phi2'.