@inproceedings{uwe2004a,
title={A Hopf differential for constant mean curvature surfaces in$S$^{2}$×R$and$H$^{2}$×R$},
author={Uwe Abresch, and Harold Rosenberg},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203345473683656},
booktitle={Acta Mathematica},
volume={193},
number={2},
pages={141-174},
year={2004},
}
Uwe Abresch, and Harold Rosenberg. A Hopf differential for constant mean curvature surfaces in$S$^{2}$×R$and$H$^{2}$×R$. 2004. Vol. 193. In Acta Mathematica. pp.141-174. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203345473683656.