We used materials from the following sources:

[1] J. Ziv and A. Lempel, IEEE Trans. IT-23, 337-343 (1977).

[2] J. A. Storer and T. G. Szymanski, J. ACM, 29, 928-951

(1982).

[3] T. C. Bell, IEEE Trans. COM-34, 1176-1182 (1986).

[4] J. Ziv and A. Lempel, IEEE Trans. IT-24, 530-536 (1978).

[5] T. A. Welch, Computer, 17, No.6, 8-19 (1984).

[6] J. A. Storer, Data Compression: Methods and Theory

(Computer Science Press, 1988).

[7] D. A. Huffman, Proc IRE 40, 1098-1101 (1952).

[8] R. Sedgewick, Algorithms, 2nd ed. (Addison-Wesley, 1988).

[9] R. G. Gallager, IEEE Trans. IT-24, 668-674 (1978).

[10] I. E. Witten, R. M. Neal, and J. G. Cleary, Commun. ACM

30, 520-540 (1987).