Section Wf_Transitive_Closure.
Variable A : Type.
Variable R : relation A.
Notation trans_clos := (clos_trans A R).
red; auto with sets.
Qed.
induction 1 as [x0 _ H1].
apply Acc_intro.
intros y H2.
induction H2; auto with sets.
apply Acc_inv with y; auto with sets.
Defined.
Hint Resolve Acc_clos_trans : core.

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