@inproceedings{henry1961prediction,
title={Prediction theory and fourier series in several variables. II},
author={Henry Helson, and David Lowdenslager},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203157772833927},
booktitle={Acta Mathematica},
volume={106},
number={3},
pages={175-213},
year={1961},
}
Henry Helson, and David Lowdenslager. Prediction theory and fourier series in several variables. II. 1961. Vol. 106. In Acta Mathematica. pp.175-213. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203157772833927.