@inproceedings{karl1978on,
title={On the number of restricted prime factors of an integer. II},
author={Karl K. Norton},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203249075986259},
booktitle={Acta Mathematica},
volume={143},
number={1},
pages={9-38},
year={1978},
}