Teturo Kamae Hui Rao Yu-Mei Xue Maximal pattern complexity of two-dimensional words. 15-27 2006 359 Theor. Comput. Sci. 1-3 http://dx.doi.org/10.1016/j.tcs.2006.02.023 db/journals/tcs/tcs359.html#KamaeRX06