Xiao Yi WANG Huashang College Guangdong University of Business Studies,Guangzhou 511300,P.R.China Ming Jun LI School of Mathematics and Computational Science,Xiangtan 411105,P.R.China
Acta Mathematica Sinica, Chinese Series
.
2009, (05): 61
-66
.
DOI: 10.12386/A2009sxxb0110
