.

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