1. G. Berman and K. D. Fryer, Introduction to Combinatorics, Academic Press, 1972.
2. D. I. A. Cohen, Combinatorial Theory, Wiley, 1978.
3. C. L. Liu, Elements of Discrete Mathematics, McGraw-Hill, 1977.
4. A. Tucker, Applied Combinatorics, Wiley, 1980.