@inproceedings{r.1975$c$^{∞}convex,
title={$C$^{∞}convex functions and manifolds of positive curvature},
author={R. E. Greene, and H. Wu},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203241348178212},
booktitle={Acta Mathematica},
volume={137},
number={1},
pages={209-245},
year={1975},
}
R. E. Greene, and H. Wu. $C$^{∞}convex functions and manifolds of positive curvature. 1975. Vol. 137. In Acta Mathematica. pp.209-245. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203241348178212.