@inproceedings{t.1936riemann,
title={Riemann spaces of class one and their characterization},
author={T. Y. Thomas},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203109019451562},
booktitle={Acta Mathematica},
volume={67},
number={1},
pages={169-211},
year={1936},
}