Sugie J, Yamaoka N. Multilayer structures of second-order linear differential equations of Euler type and their application to nonlinear oscillations. Ukr. Mat. Zhurn. [Internet]. 2006Dec.25 [cited 2024Apr.25];58(12):1704–1714. Available from: https://umj.imath.kiev.ua/index.php/umj/article/view/3566