Section CONGRUENT_STRICT_TRIANGLES.
Definition CongruentStrictTriangles (A B C A' B' C' : Point) :=
CongruentTriangles A B C A' B' C' /\
~Collinear A B C.

Lemma ClockwiseEq : forall A B C D : Point,
Clockwise A B C ->
Collinear A B D ->
Collinear B C D ->
B = D.