A = (-0.1, 1.4)
B = (13.1, 1.4)
U = Midpoint(A, B)
c = Semicircle(A, B)
C = Point(c)
P, a, b, d = Polygon(A, B, C)
e = Segment(C, U)
α = Angle(B, A, C)
γ_1 = Angle(A, C, U)
β = Angle(C, B, A)
γ_2 = Angle(U, C, B)