A = (1, 1)
B = (2, 3)
C = (5, 3)
D = (5, 1)
poly1, a, b, c, d = Polygon(A, B, C, D)
α = Angle(C, D, A)
e = OrthogonalLine(B, d)
E = Intersect(e, d)
f = Segment(B, E)
β = Angle(D, E, B)