.

                                    P
                           u     s   s       u
                        s         y   P          s
                       s            u               s
                      y             s                y
                     P              s                  P
                    u               y                  u
                    s            P      u               s
                    s           s          s              s
                    y             y      P              y
                      P               u                 P
                         u             s              u
                              s         s          s
                                   s   y   s