proposition: Lemma bet_cop__cop : forall A B C D E, Coplanar A B C E -> Bet C D E -> Coplanar A B C D.
proof: Proof. intros A B C D E HCop HBet. destruct (eq_dec_points C E). treat_equalities; apply HCop. apply col_cop__cop with E; Col. Qed.
imports: GeoCoq.Tarski_dev.Ch08_orthogonality GeoCoq.Tarski_dev.Annexes.coplanar