@inproceedings{claus2009a,
title={A general existence proof for non-linear elliptic equations in semi-Riemannian spaces},
author={Claus Gerhardt},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20161002033538270043059},
booktitle={Amer.J. Math.},
volume={131},
number={6},
pages={1569 - 1588},
year={2009},
}

Claus Gerhardt. A general existence proof for non-linear elliptic equations in semi-Riemannian spaces. 2009. Vol. 131. In Amer.J. Math.. pp.1569 - 1588. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20161002033538270043059.