Section T11_2.
Context `{TnEQD:Tarski_neutral_dimensionless_with_decidable_point_equality}.
(** This is exterior angle theorem *)

Lemma not_conga : forall A B C A' B' C' D E F ,
CongA A B C A' B' C' ->
~ CongA A B C D E F ->
~ CongA A' B' C' D E F.