1. Dept. of Applied Mathematics, Nanjing University of Science and Technology, Nanjing, P. R. China + School of Science, Qilu University of Technology, Jinan, P. R. China%SR92-01.45
2. Faculty of Mathematics, Kim Tl Sung University, Pyongyang, Democratic People's Republic of Korea%SR92-01.44
3. Dept. of Applied Mathematics, Nanjing University of Science and Technology, Nanjing, P. R. China%SR92-01.45