Section Sums.
Context `{TnEQD:Tarski_neutral_dimensionless_with_decidable_point_equality}.
(** Existence of the sum *)
(** Commutativity of the sum. *)
(** Unicity of the sum. *)
(** Unicity of the difference of segments. *)

Lemma sums2__cong12 : forall A B C D E F A' B', SumS A B C D E F -> SumS A' B' C D E F ->
Cong A B A' B'.