Marcella Anselmo, Dora Giammarresi, Maria Madonia. Regular Expressions for Two-Dimensional Languages Over One-Letter Alphabet. In Cristian Calude, Elena Calude, Michael J. Dinneen, editors, Developments in Language Theory, 8th International Conference, DLT 2004, Auckland, New Zealand, December 13-17, 2004, Proceedings. Volume 3340 of Lecture Notes in Computer Science, pages 63-75, Springer, 2004. [doi]
Abstract is missing.