@inproceedings{david1971approximation,
title={Approximation of the Dirichlet problem on a half space},
author={David G. Schaeffer},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203226664536140},
booktitle={Acta Mathematica},
volume={129},
number={1},
pages={281-295},
year={1971},
}