.

                                      F
                      ­         i      ir      i
                            r         e          r
                           e          F           e
                          F         i   r          F
                          i         e    F          i
                          r         r    e          r
                           e        F   i           e
                            F        r e           F
                              i         F          i
                                r       i         r
                                  e     r      e
                                         e