Makoto Sakamoto and Yasuo Uchida and Makoto Nagatomo and Takao Ito and Tsunehiro Yoshinaga and Satoshi Ikeda and Masahiro Yokomichi and Hiroshi Furutani, Hierarchies Based On the Number of Cooperating Systems of Finite Automata on Four-Dimensional Input Tapes. journal = {International Journal of Mathematical and Computational Sciences}, [online]. World Academy of Science, Engineering and Technology. December 2012, vol. 72(12). 1707 - 1712 [viewed 23 September 2024]. Available from: https://publications.waset.org/pdf/6351.