12 In N N g A1B2…B g A21B2 g 2k B 2 kk    =             =             1 2 11 12 1 21 22 2 1 2     g  n n g g gn           =                      11 12 1 21 22 2 1 2     g g g g gg  =                      11 12 1 21 22 2 1 2     k k k k kk