中国科学院数学与系统科学研究院期刊网
How to Recognize Nonexpansive Mappings and Isometric Mappings
Guang Gui DING, Yu Mei MA
Acta Mathematica Sinica . 2011, (10): 1959 -1966 .  DOI: 10.1007/s10114-011-9470-7