Section T7_2.
Context {Tn:Tarski_neutral_dimensionless}.
Context {TnEQD:Tarski_neutral_dimensionless_with_decidable_point_equality Tn}.
(** This is Krippen lemma , proved by Gupta in its PhD in 1965 as Theorem 3.45 *)

Lemma cong_cong_half_1 : forall A M B A' M' B',
Midpoint M A B -> Midpoint M' A' B' ->
Cong A B A' B' -> Cong A M A' M'.