proposition: Lemma Par_strict_cases : forall A B C D, Par_strict A B C D \/ Par_strict B A C D \/ Par_strict A B D C \/ Par_strict B A D C \/ Par_strict C D A B \/ Par_strict C D B A \/ Par_strict D C A B \/ Par_strict D C B A -> Par_strict A B C D.
proof: Proof. intros. decompose [or] H; eauto with par. Qed.
imports: GeoCoq.Tarski_dev.Ch11_angles