A = (0.68, -0.18)
B = (6.92, 1.66)
f = Line(A, B)
g = OrthogonalLine(B, f)
S_2 = Point(g)
k_2 = Circle(S_2, B)
S_1 = Point(g)
k_1 = Circle(S_1, B)
S = Point(g)
e = Circle(S, B)
a = 0 (slider from 0 to 2, step 1)