.
                                          I
                   ­              R     RL     R
                               L        IR        L
                              I           I.           I
                              R      I     R        R
                              L       L    I         L
                               I        R  L         I
                                R        I          R
                                   l       R       I
                                      R   L   R
                                            ~
                 ­                           L