Lemma C4d : forall A B C D F E E' : Point, A <> B -> A <> C -> D <> F -> D <> E -> D <> E' -> ~Clockwise D F E -> ~Clockwise D F E' -> (Angle B A C) = (Angle E D F) -> (Angle B A C) = (Angle E' D F) -> Superimposed (HalfLine D E) (HalfLine D E').