@inproceedings{williamthe,
title={The equivariant Dehn's lemma and loop theorem},
author={William H Meeks, and Shing-Tung Yau},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20191224203730069125077},
booktitle={Commentarii Mathematici Helvetici},
volume={56},
number={1},
pages={225-239},
}

William H Meeks, and Shing-Tung Yau. The equivariant Dehn's lemma and loop theorem. Vol. 56. In Commentarii Mathematici Helvetici. pp.225-239. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20191224203730069125077.