1. Arora, S., Lund, C., Motwani, R., Sudan, M., Szegedy, M.: Proof verification and the hardness of approximation problems. J. ACM 45(3), 501–555 (1998)
2. Ausiello, G., Crescenzi, P., Gambosi, G., Kann, V., Marchetti-Spaccamela, A., Protasi, M.: Complexity and Approximation—Combinatorial Optimization Problems and Their Approximation Properties. Springer, Berlin (1999)
3. Bazgan, C.: Schémas d’approximation et complexité paramétrée, Rapport de stage de DEA d’Informatique, Université Paris-Sud, Orsay (1995)
4. Cai, L., Chen, J.: On fixed-parameter complexity and approximability of NP optimization problems. J. Comput. Syst. Sci. 54(3), 465–474 (1997)
5. Cai, L., Fellows, M., Juedes, D., Rosamond, F.: The complexity of polynomial-time approximation. Theory Comput. Syst. 41(3), 459–477 (2007)