assert(HH0:= H0).
assert(HH1:= H1).
unfold Midpoint in H0.
unfold Midpoint in H1.
spliter.
induction(eq_dec_points A B).
subst B.
apply between_identity in H0.
subst B'.
apply between_trivial2.
assert(A <> C).
intro.
subst C.
apply between_identity in H1.
subst C'.
apply between_identity in H.
contradiction.
assert(A <> B').
intro.
subst B'.
apply cong_symmetry in H3.
apply cong_identity in H3.
contradiction.
assert(A <> C').
intro.
subst C'.
apply cong_symmetry in H2.
apply cong_identity in H2.
contradiction.
assert(Col A B' C').
apply bet_col in H0.
apply bet_col in H1.
apply bet_col in H.
ColR.
induction H8.
assumption.
induction H8.
apply between_symmetry in H8.
assert(Bet A C B).
eapply bet_double_bet.
apply HH1.
apply HH0.
assumption.
assert(B = C).
eapply between_equality.
apply between_symmetry.
apply H9.
Between.
subst C.
assert(B' = C').
eapply l7_17.
apply HH0.
assumption.
subst C'.
apply between_trivial.
(***********************************)
assert(Bet A B' C).
eapply between_exchange4.
apply H0.
assumption.
assert(Out A B' C').
unfold Out.
repeat split; auto.
eapply l5_3.
apply H9.
assumption.
eapply l6_4_1 in H10.
spliter.
apply between_symmetry in H8.
contradiction.
Qed.

(* Specifications: *)
Lemma midpoint_preserves_bet : forall A B C B' C', Midpoint B' A B -> Midpoint C' A C -> (Bet A B C <-> Bet A B' C').
intros.