(** (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'.

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.