A. K. Prykarpatsky, A. M. Samoilenko, and V. G. Samoilenko, “Lyapunov–Schmidt Approach to Studying Homoclinic Splitting in Weakly Perturbed Lagrangian and Hamiltonian Systems”, Ukr. Mat. Zhurn., vol. 55, no. 1, pp. 66–74, Jan. 2003, Accessed: Apr. 09, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/3888