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 = Circle(D, a / 3)
E = Midpoint(f)
F = Midpoint(j)
H = Midpoint(E, D)
k = Segment(D, E)
l = Line(A, H)
m = Line(F, B)
G = Intersect(l, m)
α = Angle(A, G, B)