apply Acc_intro.
intros y H2.
induction H2; auto with sets.
apply Acc_inv with y; auto with sets.
Defined.
#[local]
Hint Resolve Acc_clos_trans : core.

(* Specifications: *)
Lemma Acc_inv_trans : forall x y:A, trans_clos y x -> Acc R x -> Acc R y.
Theorem wf_clos_trans : well_founded R -> well_founded trans_clos.