M.O. Albertson & J.P. Hutchinson,  Discrete Mathematics with Algorithms,

     Wiley, 1988.

  R. Graham, D. Knuth & O. Patashnik,  Concrete Mathematics,  Addison-

    Wesley, 1989.

   N. L. Biggs,   Discrete  Mathematics,  Oxford Science Publications, 1989.

   R.C. Bose & B. Manvel, Introduction to Combinatorail Theory, Jhon Wiley &

   Sons, 1884.