proposition: Theorem ordering_function_unicity : fun_equiv f1 f2 A1 A2.
proof: Proof. split. - split. + intros x Hx; case (A1_A2 O1 O2 _ Hx);auto. + intros x Hx; destruct (A2_A1 Hx);auto. - intros a Ha; destruct (A1_A2 O1 O2 a Ha);auto. Qed.
imports: ZornsLemma(CountableTypes)