.

                                       T
                            r        r o          r
                         o           l l              o
                       l               T                 l
                      T               r                  T
                      r               o                   r
                      o            l      l               o
                       l            T     r               l
                        l            o    l               l
                         T           l   T            T
                           r          r  o          r
                              o       ­  l          o
                                 l       L      l