@inproceedings{luis1976the,
title={The regularity of free boundaries in higher dimensions},
author={Luis A. Caffarelli},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203243427801226},
booktitle={Acta Mathematica},
volume={139},
number={1},
pages={155-184},
year={1976},
}