a(x, y) = sqrt(x^(2) + y^(2) - 1)
b(x, y) = sqrt(x^(2) + y^(2))
c(x, y) = sqrt(x^(2) + y^(2) + 1)
d(x, y) = (-a(x, y))
e(x, y) = (-b(x, y))
f(x, y) = (-c(x, y))