1. Anselmo, M., Giammarresi, D., Madonia, M., Restivo, A.: Unambiguous recognizable two-dimensional languages. R.A.I.R.O.—Inf. Théor. Appl. 40, 277–293 (2006)
2. EATCS Monographs on Theoretical Computer Science;J. Berstel,1988
3. Blum, M., Hewitt, C.: Automata on a 2-dimensional tape. In: IEEE Symposium on Switching and Automata Theory, pp. 155–160 (1967)
4. Bozapalidis, S., Grammatikopoulou, A.: Recognizable picture series. In: Droste M., Vogler H. (eds.) Special Issue on Weighted Automata, Presented at WATA 2004, Dresden, Journal of Automata, Languages and Combinatorics, vol. 10, pp. 159–183 (2005)
5. Choffrut, C., Durak, B.: Collage of two-dimensional words. Theor. Comput. Sci. 340(1), 364–380 (2005)