@inproceedings{james1959a,
title={A new definition of the integral for non-parametric problems in the calculus of variations},
author={James Serrin},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203152397124887},
booktitle={Acta Mathematica},
volume={102},
number={1},
pages={23-32},
year={1959},
}
James Serrin. A new definition of the integral for non-parametric problems in the calculus of variations. 1959. Vol. 102. In Acta Mathematica. pp.23-32. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203152397124887.