.

                                      R
                      ­       a     a   g      a
                          g         e  R          g
                         e            a               e
                       R              g                R
                       a               e                 a
                       g           R      a             g
                        e           g     e             e
                          R         R   a            R
                            a           g            a
                               g        e         g
                                   e    R      e  
                                         a
                                         g
                                         e