@inproceedings{edgar1967fréchet,
title={Fréchet differentiability of convex functions},
author={Edgar Asplund},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203215079073058},
booktitle={Acta Mathematica},
volume={121},
number={1},
pages={31-47},
year={1967},
}