@inproceedings{john2000continuity,
title={Continuity and differentiability of Nemytskii operators on the Hardy space $$\mathcal{H}^{1,1} (T^1 )$$ },
author={John F. Toland},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203603023154778},
booktitle={Arkiv for Matematik},
volume={39},
number={2},
pages={383-394},
year={2000},
}

John F. Toland. Continuity and differentiability of Nemytskii operators on the Hardy space $$\mathcal{H}^{1,1} (T^1 )$$ . 2000. Vol. 39. In Arkiv for Matematik. pp.383-394. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203603023154778.