@inproceedings{j.1957on,
title={On non-linear differential equations of the second order: III. The equation $$\ddot y - k(1 - y^2 )\dot y + y = b \mu k cos (\mu t + \alpha )$$ for large$k$, and its generalizationsfor large$k$, and its generalizations},
author={J. E. Littlewood},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203147377108851},
booktitle={Acta Mathematica},
volume={97},
number={1},
pages={267-308},
year={1957},
}
J. E. Littlewood. On non-linear differential equations of the second order: III. The equation $$\ddot y - k(1 - y^2 )\dot y + y = b \mu k cos (\mu t + \alpha )$$ for large$k$, and its generalizationsfor large$k$, and its generalizations. 1957. Vol. 97. In Acta Mathematica. pp.267-308. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203147377108851.