(** Five segments configuration. *)

Definition FSC := fun A B C D A' B' C' D' =>
  Col A B C /\ Cong_3 A B C A' B' C' /\ Cong A D A' D' /\ Cong B D B' D'.

(* Specifications: *)
Lemma l4_16 : forall A B C D A' B' C' D', FSC A B C D A' B' C' D' -> A<>B -> Cong C D C' D'.
Lemma l4_17 : forall A B C P Q, A<>B -> Col A B C -> Cong A P A Q -> Cong B P B Q -> Cong C P C Q.
Lemma l4_18 : forall A B C C', A<>B -> Col A B C -> Cong A C A C' -> Cong B C B C' -> C=C'.
Lemma l4_19 : forall A B C C', Bet A C B -> Cong A C A C' -> Cong B C B C' -> C=C'.