(** The accessibility predicate is defined to be non-informative *)
 (** (Acc_rect is automatically defined because Acc is a singleton type) *)

 Inductive Acc (x: A) : Prop :=
     Acc_intro : (forall y:A, R y x -> Acc y) -> Acc x.(** The accessibility predicate is defined to be non-informative *)
 (** (Acc_rect is automatically defined because Acc is a singleton type) *)

 Inductive Acc (x: A) : Prop :=
     Acc_intro : (forall y:A, R y x -> Acc y) -> Acc x.

Lemma Acc_inv : forall x:A, Acc x -> forall y:A, R y x -> Acc y.