M. Sassa, H. Ishizuka, M. Sawatani, and I. Nakata. Technical Report, ISE-TR-90-82. Institute of Information Sciences. An International Journal and Electronics,
University of Tsukuba, Ibaraki-ken, (June 1990)
M. Sassa, H. Ishizuka, and I. Nakata. tech. memo, PL-7. Institute of Information Sciences. An International Journal, University
of Tsukuba, Ibaraki-ken, (1985)