.

                                      P
                      ­        r      re       r
                           e         si           e
                          s           d             s
                         i           e  n            i
                        d          t     P           d
                         e          r    e           e
                          n          s  i            n
        ­                    t         d e           t
                              P        n         P
                                r       t        r
                                  e    P     e
                                        S