(* I2 : Every line contains at least two points. *)

(* Specifications: *)
Lemma I2 : forall F : Figure, forall D : Line F, exists A : Point, exists B : Point, A <> B /\ F A /\ F B.
(* I3 : There exist three noncollinear points (that is, three points not all contained in a single line). *)
Lemma I3 : exists A : Point, exists B : Point, exists C : Point, forall F : Figure, forall D : Line F, ~(F A /\ F B /\ F C).
End INCIDENCE.