a = 4.7 (slider from 0 to 10, step 0.1)
A = (0, -2)
B = Point(Circle[A, a])
f = Segment(A, B)
poly1, g, h, i, j, C, D = Polygon(A, B, 4)
c = Circle(C, a / 3)
E = Intersect(c, i)
d = Circle(E, a / 3)
F_1, G = Intersect(d, i)
e = Circle(D, a / 3)
F = Intersect(e, j)
k = Circle(F, a / 3)
I, J = Intersect(k, j)
l = Line(B, E)
m = Line(C, F)
H = Intersect(m, l)
α = Angle(F, H, B)