1. Graph Theory: An Algorithmic Approach;Chrisofiedes,1975
2. Non-isomorphic Steiner quadruple systems;Doyen;Bull. Soc. Math. Belg.,1971
3. Algorithmic Combinations;Even,1973
4. Computers and Intractability: A Guide to the Theory of NP-Completeness;Garey,1979
5. Combinatorial Theory;Hall,1967