About author:XU Zhi-cai（1958－）,male,native of Shouxian,Anhui,a professor of Huainan Institute of Technology,engages in differential geometry；XU Sen-lin（1943－）,male,native of Wuxian,Jiangsua professor of University of Science and Technology of China,engages in differential geometry and topology．
Supported by:
Supported by the National Natural Science Foundation of China（1997108）
