Winkelsummensatz
Author: Haftendorn
Date: 2007

A = (-1.8077777777777786, -0.5988888888888892)
B = (8.690404040404044, -2.004343434343434)
C = (3.126767676767679, 4.832020202020202)
poly1, c, a, b = Polygon(A, B, C)
α = Angle(B, A, C)
β = Angle(C, B, A)
γ = Angle(A, C, B)
d = Line(C, c)
D = Point(d)
E = Point(d)
δ = Angle(D, C, A)
ε = Angle(B, C, E)