@inproceedings{linda1965canonical,
title={Canonical polygons for finitely generated Fuchsian groups},
author={Linda Keen},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203207544456002},
booktitle={Acta Mathematica},
volume={115},
number={1},
pages={1-16},
year={1965},
}