Section SUPPLEMENTARY_ANGLES.
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 CongruentOpposedTriangles : forall A B C D I : Point,
Between A I C ->
Between B I D ->
Distance I A = Distance I C ->
Distance I B = Distance I D ->
CongruentTriangles A I B C I D.