.
                                  P
                           ­       U
                                   S
                                   S
                                   Y
                                   P
                                   U
                                   S
                                   S
                                   Y
                                   P
                          ­         U
                                   S
                 ­                  S
                                   Y
        ­                           P
                                   U­
                                   S
                           ­        S
                                B  l  o
                            L     o n   n
                          O      n d       d
                        N        d  e         e
                       D          e B           B
                      E          B     l           l
                      B          l       o         o
                      L          o      n         n
                       O          n  d           d
                          N        d e         e
                             D      e B      l
                                 E  o  n  d
                                        e