@inproceedings{a.1937completely,
title={Completely integrable differential equations in abstract spaces},
author={A. D. Michal, and V. Elconin},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203109925583569},
booktitle={Acta Mathematica},
volume={68},
number={1},
pages={71-107},
year={1937},
}
A. D. Michal, and V. Elconin. Completely integrable differential equations in abstract spaces. 1937. Vol. 68. In Acta Mathematica. pp.71-107. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203109925583569.