.
                                     D
                             e      e e       e
                           e        P D        e
                          p         e e           p
                         D           p             D
                         e         D     e         e
                          e        e      p         e
                           P       D     e        p
                            D       e   p       D
                              e        D         e
                                e      e       e
                                    p  e   p
                                        P