.
                                   Y
                         i       i   n       i
                      n         Y   i          n
                     Y             n             Y
                     i              Y               i
                   n               i                 n
                   Y               n                Y
                   i              Y  i               i
                    n           n   Y            n
                     Y           i  n            Y
                       i            Y            i
                          n        i ­        n
                                    n