Lemma C4c : forall A B C D F E E' : Point, A <> B -> A <> C -> D <> F -> D <> E -> D <> E' -> ~Clockwise D E F -> ~Clockwise D E' F -> Angle B A C = Angle E D F -> Angle B A C = Angle E' D F -> Superimposed (HalfLine D E) (HalfLine D E').