.
                                        P
                     ­           u    u i      u
                              i        s s         i
                             s          a           s
                            s         n    t         s
                            a        p     u        a
                            n        s     s        n
                              t        a   n        t
                                p        t         p
                                  u      P      u
             ­                        i           i