@inproceedings{antoine1992subsolutions,
title={Subsolutions and supersolutions in a free boundary problem},
author={Antoine Henrot},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203542311448616},
booktitle={Arkiv for Matematik},
volume={32},
number={1},
pages={79-98},
year={1992},
}
Antoine Henrot. Subsolutions and supersolutions in a free boundary problem. 1992. Vol. 32. In Arkiv for Matematik. pp.79-98. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203542311448616.