.
                                        P
                                r      r e       r
                             e        P r           e
                            y         e y             y
                           P           Pr              P
                           r           e   y            r
                           e          P    r            e
                            y          e   y           y
                              P        P  r           P
                                 r        e           r
                                   e      y       e
                                           Y