M = (-5, 1)
A_1 = (-10, 1)
f = Line(A_1, M)
r = 3.7 (slider from 0 to 5)
c = Circle(M, r)
A, B = Intersect(c, f)
d = Semicircle(A, B)
g = Segment(A, B)
D = Point(d)
C = Point(d)
h = Segment(M, D)
i = Segment(A, C)
S = Intersect(h, i)
α = Angle(C, S, D)