proposition: Lemma not_conga_is_anga : forall A B C A' B' C' a , ~ CongA A B C A' B' C' -> Ang_Acute A B C a -> ~(a A' B' C').
proof: Proof. intros. unfold Ang_Acute in H0. spliter. intro. apply H. apply (anga_conga a); auto. Qed.
imports: GeoCoq.Tarski_dev.Ch13_2_length Setoid