@inproceedings{karsten1991volume,
title={Volume comparison à la Aleksandrov},
author={Karsten Grove, and Peter Petersen},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203318644128474},
booktitle={Acta Mathematica},
volume={169},
number={1},
pages={131-151},
year={1991},
}