Akira Ito, Katsushi Inoue, Itsuo Takanami. Complexity of Acceptance Problems for Two-Dimensional Automata. In R. Narasimhan, editor, A Perspective in Theoretical Computer Science - Commemorative Volume for Gift Siromoney. Volume 16 of World Scientific Series in Computer Science, pages 70-94, World Scientific, 1989. [doi]
Abstract is missing.