Inductive Point :=
  P0 | P1 | P2 | P3.Inductive Point :=
  P0 | P1 | P2 | P3.Inductive Point :=
  P0 | P1 | P2 | P3.Inductive Point :=
  P0 | P1 | P2 | P3.Inductive Point :=
  P0 | P1 | P2 | P3.Definition Bet (A B C : Point) :=
  A = B \/ B = C \/ A = C.Definition Cong (A B C D : Point) :=
  (A = B /\ C = D) \/ (A <> B /\ C <> D).

Lemma cong_identity : forall A B C, Cong A B C C -> A = B.