@inproceedings{w.1949sur,
title={Sur les correspondances multivoques entre deux ensembles abstraits},
author={W. Simonsen},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203126118954693},
booktitle={Acta Mathematica},
volume={81},
number={1},
pages={291-297},
year={1949},
}