.
                                  M
                           ­  a   ag    a
                            g    i c      g
                           i      M        i
                          c        a          c
                ­        M        g          M
                       a           i            a
                      g            c             g
                     i           M a            i
                     c          g    i            c
                    M        c    ­ M         M
                      a        a     g         a
                        g        i    c        g
              ­              i      M       i
                                c   a   c
                                     g
                                     i
                        ­             c