Section MIDLINE.
Definition MidLineDef (A B : Point) : Figure :=
fun M : Point => Distance M A = Distance M B.

Lemma CollinearMidLine : forall A B C D M : Point,
A <> B ->
Distance C A = Distance C B ->
Clockwise A B C ->
Distance D A = Distance D B ->
Clockwise B A D ->
Collinear C D M ->
Distance M A = Distance M B.