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 *)

Lemma cong3_sums__sums : forall A B C D E F A' B' C' D' E' F',
Cong A B A' B' -> Cong C D C' D' -> Cong E F E' F' -> SumS A B C D E F ->
SumS A' B' C' D' E' F'.