1. Y.X. Luo, L.T. Zhang and M. Li: Grey systems and applications in mechanical engineering (National University of Defence Technology Press, Changsha, 2001).
2. Y. Mu: System Engineering and Electronics, Vol. 25, No. 9 (2003), p.1094.
3. Z.X. Wang, Y.G. Dang and S.F. Liu: Systems Engineering - Theory & Practice, Vol. 29, No. 10 (2009), p.138.
4. Z.M. Song, J.L. Deng: Systems Engineering, Vol. 19, No. 1 (2001), p.66.
5. Y.G. Dang, S.F. Liu and B. Liu: Chinese Journal of Management Science, Vol. 13, No. 1 (2005), p.132.