@inproceedings{harold1968smoothness,
title={Smoothness of the boundary function of a holomorphic function of bounded type},
author={Harold S. Shapiro},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203440768151098},
booktitle={Arkiv for Matematik},
volume={7},
number={5},
pages={443-447},
year={1968},
}
Harold S. Shapiro. Smoothness of the boundary function of a holomorphic function of bounded type. 1968. Vol. 7. In Arkiv for Matematik. pp.443-447. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203440768151098.