Require Export GeoCoq.Tarski_dev.Ch06_out_lines.
Section Sums.
Context `{TnEQD:Tarski_neutral_dimensionless_with_decidable_point_equality}.
(** Existence of the sum *)

(** Commutativity of the sum. *)
Lemma sums_sym : forall A B C D E F, SumS A B C D E F -> SumS C D A B E F.