Section Euclid_to_Tarski.
Context `{Ax:euclidean_neutral_ruler_compass}.
Definition Bet A B C := BetS A B C \/ A=B \/ B=C.
Definition TCong A B C D := Cong A B C D \/ (A=B /\ C=D).

Lemma cong_sym : forall A B C D, Cong A B C D -> Cong C D A B.