1. The Boolean hierarchy: hardware over NP;Cai,1986
2. Graph minimal uncolorability is DP-complete;Cai;SIAM J. Comput.,1986
3. Computers and Intractibility: A Guide to the Theory of NP-Completeness;Garey,1979
4. Some simplified NP-complete graph problems;Garey;Theoret. Comput. Sci.,1976