S_1 = (19.52, -4.66)
B = (11, -4.08)
k_1 = Circle(S_1, B)
S_2 = (21.94, -4.64)
D = (18.04, -3.78)
k_2 = Circle(S_2, D)
f = Line(S_1, S_2)
A = Intersect(k_2, f, 1)
a = 0 (slider from 0 to 3, step 1)
C = Intersect(k_1, f, 1)
E = Intersect(k_1, f, 2)
S_3 = Midpoint(C, A)
S_4 = Midpoint(A, E)
k_4 = Circle(S_4, A)
k_3 = Circle(S_3, A)