proposition: Lemma swap_Acc : forall x y:A, Acc SwapProd (x, y) -> Acc SwapProd (y, x).
proof: Proof. intros. inversion_clear H. apply Acc_intro. destruct y0; intros. inversion_clear H; inversion_clear H1; apply H0. - apply sp_swap. apply right_sym; auto with sets. - apply sp_swap. apply left_sym; auto with sets. - apply sp_noswap. apply right_sym; auto with sets. - apply sp_noswap. apply left_sym; auto with sets. Defined.
imports: EqdepFacts Relation_Operators Transitive_Closure Inclusion Inverse_Image