@inproceedings{fabrice1990the,
title={The approximation problem for Sobolev maps between two manifolds},
author={Fabrice Bethuel},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203316896401461},
booktitle={Acta Mathematica},
volume={167},
number={1},
pages={153-206},
year={1990},
}
Fabrice Bethuel. The approximation problem for Sobolev maps between two manifolds. 1990. Vol. 167. In Acta Mathematica. pp.153-206. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203316896401461.