Shigeru Watanabe. Periodicity of Post's normal process of tag. Proceedings of the Symposium on Mathematical Theory of Automata, New York, N.Y., April 24, 25, 26, 1962, Microwave Research Institute symposia series vol. 12, Polytechnic Press of the Polytechnic Institute of Brooklyn, Brooklyn, N.Y., 1963, pp. 83–99.
Mary Katherine Yntema · Journal of Symbolic Logic · 1968
Shigeru Watanabe. Periodicity of Post's normal process of tag. Proceedings of the Symposium on Mathematical Theory of Automata, New York, N.Y., April 24, 25, 26, 1962, Microwave Research Institute symposia series vol. 12, Polytechnic Press of the Polytechnic Institute of Brooklyn, Brooklyn, N.Y., 1963, pp. 83–99. - Volume 33 Issue 2