2D PSS (y,ẏ, for x = 0 and $\dot{x}<0$) of planar orbits for energy level E_j = −4.0 (black). The (y,ẏ) projections of the 4D PSS of the first 20 000 iterations of three 3D sticky chaotic orbits having a small third dimension z = 0.02 above the plane of rotation are plotted in colour. The red one behaves like a regular orbit and the green one like a weakly chaotic orbit for very long times. The blue one is diffused rather quickly outwards.