@inproceedings{j.1957on,
title={On non-linear differential equations of the second order. III. The equation $$\ddot y - k\left( {1 - y^2 } \right)\dot y + y = b\mu k$$ cos (μt+α) for large k, and its generalizationscos (μt+α) for large k, and its generalizations},
author={J. E. Littlewood},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203147654745853},
booktitle={Acta Mathematica},
volume={98},
number={1},
pages={110-110},
year={1957},
}

J. E. Littlewood. On non-linear differential equations of the second order. III. The equation $$\ddot y - k\left( {1 - y^2 } \right)\dot y + y = b\mu k$$ cos (μt+α) for large k, and its generalizationscos (μt+α) for large k, and its generalizations. 1957. Vol. 98. In Acta Mathematica. pp.110-110. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203147654745853.