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