proposition: Lemma acute_obtuse__lta : forall A B C D E F, Acute A B C -> Obtuse D E F -> LtA A B C D E F.
proof: Proof. intros A B C D E F Hacute Hobtuse. destruct Hacute as [G [H [I [HPer Hlta]]]]. apply (lta_trans _ _ _ G H I); auto. apply lta_distincts in Hlta. spliter. apply obtuse_per__lta; auto. Qed.
imports: GeoCoq.Tarski_dev.Ch10_line_reflexivity_2