proposition: Lemma cong_dec_eq_dec_b : (forall A B:Tpoint, ~ A <> B -> A = B).
proof: Proof. intros A B HAB. apply cong_identity with A. apply Cong_stability. intro HNCong. apply HAB. intro HEq. subst. apply HNCong. apply cong_pseudo_reflexivity. Qed.
imports: GeoCoq.Tarski_dev.Ch02_cong