@inproceedings{friedrich1967extremal,
title={Extremal elements in certain classes of conformal mappings of an annulus},
author={Friedrich Huckemann},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203211853565036},
booktitle={Acta Mathematica},
volume={118},
number={1},
pages={193-221},
year={1967},
}
Friedrich Huckemann. Extremal elements in certain classes of conformal mappings of an annulus. 1967. Vol. 118. In Acta Mathematica. pp.193-221. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203211853565036.