Definition Supplementary (alpha beta : AS) :=
exists A  : Point,  exists B  : Point,  exists C : Point,  exists D : Point, 
	A <> C /\ Between B A D /\ Angle B A C = alpha /\ Angle C A D = beta.

Lemma HalfLineBetweenBetween : forall A B C D : Point, Between A C D -> HalfLine C A B -> Between B C D.