@inproceedings{george1922surface,
title={Surface transformations and their dynamical applications},
author={George D. Birkhoff},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203036362953309},
booktitle={Acta Mathematica},
volume={43},
number={1},
pages={1-119},
year={1922},
}