V. N. Koshlyakov, “Method of averaging in the problem of stability of motion of a body suspended from a string”, Ukr. Mat. Zhurn., vol. 59, no. 4, pp. 467–475, Apr. 2007, Accessed: Apr. 09, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/3321