@inproceedings{james1964the,
title={The functional equation$f$^{$n$}($x$)=$g$($x$)},
author={James C. Lillo},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203432241956026},
booktitle={Arkiv for Matematik},
volume={5},
number={3},
pages={357-361},
year={1964},
}