(** (Outer) Five segments configuration. *)

Definition OFSC := fun A B C D A' B' C' D' => 
  Bet A B C /\ Bet A' B' C' /\ 
  Cong A B A' B' /\ Cong B C B' C' /\ 
  Cong A D A' D' /\ Cong B D B' D'.

(* Specifications: *)
Lemma five_segments_with_def : forall A B C D A' B' C' D', OFSC A B C D A' B' C' D' -> A<>B -> Cong C D C' D'.
Lemma l2_11 : forall A B C A' B' C', Bet A B C -> Bet A' B' C' -> Cong A B A' B' -> Cong B C B' C' -> Cong A C A' C'.
Lemma construction_unicity : forall Q A B C x y, ~(Q=A) -> Bet Q A x -> Cong A x B C -> Bet Q A y -> Cong A y B C -> x=y.