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 *)
(** Some permutation properties *)
(** Basic case of sum *)
(** Associativity of the sum. *)
(** AB <= AB + CD *)
(** CD <= AB + CD *)
(** If the sum of two segments is degenerate, then the segments are degenerate *)
(** SumS preserves Le *)
(** If AB <= A'B', CD <= C'D' and AB + CD = A'B' + C'D', then AB = A'B' and CD = C'D' *)

Lemma le2_sums2__cong12 : forall A B C D E F A' B' C' D',
Le A B A' B' -> Le C D C' D' -> SumS A B C D E F -> SumS A' B' C' D' E F ->
Cong A B A' B'.