proposition: Lemma ord_eq (A : Ensemble Ord) (f : Ord -> Ord) : ordering_function f A B -> fun_equiv f (ord B) A (the_ordering_segment B).
proof: Proof. Proof with eauto with schutte. intros;eapply ordering_function_unicity... apply ord_ok. Qed.
imports: ZornsLemma(CountableTypes)