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. *)
(** Unicity of the difference of segments on the right. *)
(** Cong preserves SumS *)
(** The degenerate segments represent the additive identity *)

Lemma sums__eq12 : forall A B C D, SumS A B C D C D -> A = B.