proposition: Lemma obtuse_suppa__acute : forall A B C D E F, Obtuse A B C -> SuppA A B C D E F -> Acute D E F.
proof: Proof. unfold SuppA. intros; spliter. ex_and H1 A'. apply (acute_conga__acute C B A'); [|apply conga_sym, H2]. apply conga_distinct in H2; spliter. apply acute_sym, (bet_obtuse__acute A); auto. Qed.
imports: GeoCoq.Tarski_dev.Ch10_line_reflexivity_2