@inproceedings{lipman1977an,
title={An extremal problem for quasiconformal mappings and a theorem by Thurston},
author={Lipman Bers},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203246678542243},
booktitle={Acta Mathematica},
volume={141},
number={1},
pages={73-98},
year={1977},
}
Lipman Bers. An extremal problem for quasiconformal mappings and a theorem by Thurston. 1977. Vol. 141. In Acta Mathematica. pp.73-98. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203246678542243.