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. *)

Lemma sums2__cong34 : forall A B C D E F C' D', SumS A B C D E F -> SumS A B C' D' E F ->
Cong C D C' D'.