Section T16.
Context `{T2D:Tarski_2D}.
Context `{TE:@Tarski_euclidean Tn TnEQD}.
(** Lemma 16.2 in dimension 2. *)
(** As we are in dimension 2, we skip 16.3 which is only needed to prove 16.4 in dimension n. *)

(** Lemma 16.6 in dimension 2. *)
Lemma Cd_Col : forall O E S U1 U2 P X Y,
Cd O E S U1 U2 P X Y -> Col O E X /\ Col O E Y.