.
                                     D
                            i       is        i
                        s          hD           s
                      h             i               h
                     D             s                D
                     i              h                 i
                     s            D  i               s
                      h          s   h             h
                       D         D   i           D
                          i         s h          i
                            s        D        s
                                h    i     h
                                      s
                                      h