proposition: Lemma between_symmetry_B : forall A B C, BetH A B C -> BetH C B A.
proof: Proof. unfold BetH. intros A B C HBet. repeat split; intuition. Qed.
imports: GeoCoq.Axioms.beeson_s_axioms GeoCoq.Tarski_dev.Ch08_orthogonality