Section T6_1.
Context `{TnEQD:Tarski_neutral_dimensionless_with_decidable_point_equality}.
(** out reflexivity. l6_5 *)
(** out symmetry. *)
(** out transitivity. *)
(** Unicity of intersection *)

Lemma l6_21 : forall A B C D P Q,
~ Col A B C -> C<>D -> Col A B P -> Col A B Q -> Col C D P -> Col C D Q -> P=Q.