.

                                     A
                             d    d   d      d
                          d        i   c          d
                        i             t                i
                       c             A                c
                       t              d                 t
                      A             d                 A
                      d           i       c            d
                       d           t     A           d
                         i             d              i
                           c          d           c
                              t        i        t
             ­                          c
                                       k