@inproceedings{g.1981$k$-functionals,
title={$K$-functionals and moduli of continuity in weighted polynomial approximation},
author={G. Freud, and H. N. Mhaskar},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203514945095389},
booktitle={Arkiv for Matematik},
volume={21},
number={1},
pages={145-161},
year={1981},
}
G. Freud, and H. N. Mhaskar. $K$-functionals and moduli of continuity in weighted polynomial approximation. 1981. Vol. 21. In Arkiv for Matematik. pp.145-161. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203514945095389.