Proof with Tarski.
intros.
assert (exists C', Bet A D C' /\ Cong D C' C D)...
DecompExAnd H2 C'.
assert (exists D', Bet A C D' /\ Cong C D' C D)...
DecompExAnd H2 D'.
(* *)
assert (exists B', Bet A C' B' /\ Cong C' B' C B)...
DecompExAnd H2 B'.
assert (exists B'', Bet A D' B'' /\ Cong D' B'' D B)...
DecompExAnd H2 B''.
assert (Cong B C' B'' C).
eapply l2_11.
3:apply cong_commutativity.
3:apply cong_symmetry.
3:apply H11.
Between.
Between.
esTarski.
assert (Cong B B' B'' B).
eapply l2_11;try apply H2;Between.
(* *)
assert (B''=B').
apply construction_unicity with
(Q:=A) (A:=B) (B:=B'') (C:=B) (x:=B'') (y:=B');Between...
smart_subst B''.
assert (FSC B C D' C' B' C' D C).
unfold FSC;repeat split;unfold Col;Between;sTarski.
Focus 2.
eapply cong_transitivity.
apply H7.
sTarski.
apply l2_11 with (A:=B) (B:=C) (C:=D') (A':=B') (B':=C') (C':=D);
Between;sTarski;esTarski.
assert (Cong C' D' C D).
cases_equality B C.
(* *)
treat_equalities.
eapply cong_transitivity.
apply cong_commutativity.
apply H11.
Tarski.
(* *)
apply cong_commutativity.
eapply l4_16;try apply H3...
(* *)
assert (exists E, Bet C E C' /\ Bet D E D').
eapply inner_pasch;Between.
DecompExAnd H13 E.
(* *)
assert (IFSC D E D' C D E D' C').
unfold IFSC;repeat split;Between;sTarski.
eapply cong_transitivity.
apply cong_commutativity.
apply H7.
sTarski.
(* *)
assert (IFSC C E C' D C E C' D').
unfold IFSC;repeat split;Between;sTarski.
eapply cong_transitivity.
apply cong_commutativity.
apply H5.
sTarski.
(* *)
assert (Cong E C E C').
eapply l4_2;eauto.
(* *)
assert (Cong E D E D').
eapply l4_2;eauto.
(* *)
cases_equality C C'.
smart_subst C'.
assert (E=C).
eTarski.
smart_subst E.
unfold IFSC, FSC,Cong_3 in *;intuition.
(* *)
assert (C<>D').
unfold not;intro.
treat_equalities...
(* *)
assert (exists P, Bet C' C P /\ Cong C P C D')...
DecompExAnd H21 P.
assert (exists R, Bet D' C R /\ Cong C R C E)...
DecompExAnd H21 R.
assert (exists Q, Bet P R Q /\ Cong R Q R P)...
DecompExAnd H21 Q.
(* *)
assert (FSC D' C R P P C E D').
unfold FSC;unfold Cong_3;intuition...
eapply l2_11.
apply H25.
3:apply H26.
Between.
sTarski.
(* *)
assert (Cong R P E D').
eapply l4_16.
apply H21.
auto.
(* *)
assert (Cong R Q E D).
eapply cong_transitivity.
apply H28.
eapply cong_transitivity.
apply H22.
sTarski.
(* *)
assert (FSC D' E D C P R Q C).
unfold FSC;unfold Cong_3;intuition...
eapply l2_11.
3:eapply cong_commutativity.
3:eapply cong_symmetry.
3:apply H22.
Between.
Between.
sTarski.
(* *)
assert (Cong D C Q C).
cases_equality D' E.
(* *)
treat_equalities...
sTarski.
(* *)
eapply l4_16;eauto.
(* *)
assert (Cong C P C Q).
unfold FSC in *;unfold Cong_3 in *;intuition.
eapply cong_transitivity.
2:apply cong_commutativity.
2:apply H31.
eapply cong_transitivity.
2:apply H7.
sTarski.
(* *)
assert (R<>C).
unfold not;intro.
(* *)
treat_equalities...
(* *)
assert (Cong D' P D' Q).
apply l4_17 with (A:=R) (B:=C) (C:=D').
assumption.
3:apply H32.
unfold Col;left;Between.
sTarski.
(* *)
assert (Cong B P B Q).
eapply  l4_17; try apply H20;auto.
unfold Col;right;right;Between.
(* *)
assert (Cong B' P B' Q).
eapply  l4_17 with (C:=B').
apply H20.
unfold Col.
Between.
assumption.
assumption.
(* *)
assert (Cong C' P C' Q).
cases_equality B B'.
(* *)
Focus 2.
(* *)
eapply l4_17.
apply H37.
unfold Col;right;left;Between.
auto.
auto.
(* *)
subst B'.
unfold IFSC,FSC, Cong_3 in *;intuition.
clean_duplicated_hyps.
clean_trivial_hyps.
(* *)
Focus 2.
(* *)
assert (Cong P P P Q).
eapply  l4_17.
apply H19.
unfold Col;right;right;Between.
auto.
auto.
(* *)
assert (P=Q).
eapply cong_identity.
apply cong_symmetry.
apply H38.
(* *)
subst Q.
assert (D=D').
eapply cong_identity with (A:=D) (B:=D') (C:=P).
unfold IFSC,FSC, Cong_3 in *;intuition.
(* *)
subst D'.
(* *)
assert (E=D).
eTarski.
unfold IFSC,FSC, Cong_3 in *;intuition.
(* *)
assert (Bet A B D').
Between.
assert (B=D').
eTarski.
treat_equalities.
Tarski.
Qed.

(* Specifications: *)
Lemma l5_2 : forall A B C D,
A<>B -> Bet A B C -> Bet A B D -> Bet B C D \/ Bet B D C.