Hi, > The xz plane (figure 1.3.1c) simply does not show up. maybe you can try \psSolid[object=plan, definition=equation, args={[0 -1 0 0]}, fillcolor=gray, incolor=red!30, base=0 5 0 5, % planmarks, % plangrid, showbase, % % grid, ] (I did'nt try). Jean-Paul