Section T15.
Context `{T2D:Tarski_2D}.
Context `{TE:@Tarski_euclidean Tn TnEQD}.
(** Lemma 15.2 *)
(** Cong corresponds to length equality.*)
(** Le corresponds to length inequality.*)
(********************************************************)

Lemma sum_preserves_ltp_rev : forall O E E' A B C AC BC, Sum O E E' A C AC -> Sum O E E' B C BC -> LtP O E E' AC BC
->  LtP O E E' A B.