Hint Resolve chara_not_2 chasles A2a A2b A3a A3b A5 A6: Geom.
(** Decidability lemmmas *)

(* Specifications: *)
Lemma eq_dec_points : forall A B:Point, A=B \/ A<>B.
Lemma col_dec : forall A B C:Point, Col A B C \/ ~ Col A B C.
Lemma parallel_dec : forall A B C D, parallel A B C D \/ ~ parallel A B C D.
Lemma number_dec : forall r: F, r=0 \/ r<>0.
Ltac cases_equality A B := elim (eq_dec_points A B);intros.