中国科学院数学与系统科学研究院期刊网
AMS
Several Remarks on Ball-Coverings of Normed Spaces
Li Xin CHENG, Zheng Hua LUO, Xue Fang LIU, Wen ZHANG
Acta Mathematica Sinica . 2010, (9): 1667 -1672 .  DOI: 10.1007/s10114-010-9036-0