z = u^4 + v^4 - 4 * u * v + 1
contour_plot(z, (u, -2, 2), (v, -2, 2), contours = (-1, -0.5, 0.5, 0.9, 1, 1.1, 1.5, 2, 2.5, 3), plot_points = 100, fill = False) + \
point([(1, 1), (-1, -1)], pointsize = 30, rgbcolor = "green") + \
point((0, 0), pointsize = 30, rgbcolor = "red")