@inproceedings{m.1982the,
title={The extension problem for certain function spaces involving fractional orders of differentiability},
author={M. Christ},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203516937941405},
booktitle={Arkiv for Matematik},
volume={22},
number={1},
pages={63-81},
year={1982},
}
M. Christ. The extension problem for certain function spaces involving fractional orders of differentiability. 1982. Vol. 22. In Arkiv for Matematik. pp.63-81. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203516937941405.