Section Suma_2.
Context `{TnEQD:Tarski_neutral_dimensionless_with_decidable_point_equality}.
(** ABC <= ABC + DEF. *)
(** DEF <= ABC + DEF. *)
(** LeA preserves SAMS. *)
(** SumA preserves LeA. *)
(** Unicity of the difference of angles. *)
(** Unicity of the difference on the left. *)
(** Associativity of the sum of angles. *)

Lemma suma_assoc : forall A B C D E F G H I K L M A' B' C' D' E' F',
SAMS A B C D E F -> SAMS D E F G H I ->
SumA A B C D E F A' B' C' -> SumA D E F G H I D' E' F' ->
(SumA A' B' C' G H I K L M <-> SumA A B C D' E' F' K L M).