F. De Carli Andrea Frosini Simone Rinaldi Andrea Sorbi Lattices of local two-dimensional languages. 2701-2713 2009 410 Theor. Comput. Sci. 27-29 http://dx.doi.org/10.1016/j.tcs.2009.03.025 db/journals/tcs/tcs410.html#CarliFRS09