f: y = sqrt(4 - x^(2))
a = 0.7 (slider from -2 to 2, step 0.01)
A: (a, 0)
B: (x(A), f(x(A)))
g = Segment(B, A)
b = Surface(a, t + y(B) / 2, (s * sqrt((y(B) / 2)^(2) - t^(2))), t, ((-y(B))) / 2, y(B) / 2, s, 0, 1)
c = Surface(t, (s * sqrt(4 - t^(2))), (sqrt(1 / 4 - (s - 1 / 2)^(2)) * sqrt(4 - t^(2))), t, -2, 2, s, 0, 1)