@inproceedings{casper1959non-parametric,
title={Non-parametric surfaces given by linearly continuous functions},
author={Casper Goffman},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203154763436906},
booktitle={Acta Mathematica},
volume={103},
number={3},
pages={269-291},
year={1959},
}

Casper Goffman. Non-parametric surfaces given by linearly continuous functions. 1959. Vol. 103. In Acta Mathematica. pp.269-291. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203154763436906.