radio

r = 3.2 (slider from -5 to 5)
b = Surface(((r * sin(t)) * cos(s)), ((r * sin(t)) * sin(s)), (((-r) * cos(t)) * lg(tan(t / 2))), t, (-pi) / 2, pi / 2, s, (-pi), pi)
a = Surface(((r * sin(t)) * cos(s)), ((r * sin(t)) * sin(s)), ((r * cos(t)) * lg(tan(t / 2))), t, (-pi) / 2, pi / 2, s, (-pi), pi)