A = (-0.1, 1.4)
B = (13.1, 1.4)
k = Semicircle(A, B)
C = Point(k)
P, c, a, b = Polygon(A, B, C)
α = Angle(B, A, C)
β = Angle(C, B, A)
γ = Angle(A, C, B)