proposition: Lemma not_obtuse_saccheris : ~ hypothesis_of_obtuse_saccheri_quadrilaterals.
proof: Proof. apply not_oah; right. unfold hypothesis_of_right_saccheri_quadrilaterals; apply right_saccheris. Qed.
imports: GeoCoq.Tarski_dev.Annexes.circles GeoCoq.Tarski_dev.Annexes.half_angles GeoCoq.Tarski_dev.Ch12_parallel_inter_dec