1. Yuchun Zhang, Chuan He and Yong Fang: China Safety Science Journal. Vol. 19 (2009), pp.120-123. (In Chinese).
2. Julong Deng: Grey Prediction and Grey Decision (Huazhong University of Science and Technology Press, Wuhan 2002). (In Chinese).
3. Xinping Xiao, Zhongmin Song and Feng Li: Grey Technology and Application (Science Press, Beijing 2005). (In Chinese).
4. Duncan T E, Pasik D B and Stettner L: Appl. Math. Optim. Vol. 37 (1998), p.37.
5. Bluementhal R M, Getoor R K: Markov Process and Potential Theory (Academy Press, New York 1986).