1. S. Akira, Y. Makoto and M. Masao, Jap. Pat. No. 44-41 239 (May 23, 1969).
2. T. Akio and M. Sindzi, Jap. Pat. No. 48-27 540 (Feb. 14, 1972).
3. S. Akira, Y. Makoto and M. Masao, Jap. Pat. No. 43-68 980 (Sept. 19, 1968).
4. T. Akio and T. Masamiti, Jap. Pat. No. 48-121 398 (Oct. 29, 1973).