Lavcel-Budko, Olga, and Aleksandras Krylovas. “Weak Resonances of Periodical Nonlinear Oscillations”. Lietuvos matematikos rinkinys 58, no. B (December 20, 2017): 51–56. Accessed December 5, 2025. https://www.journals.vu.lt/LMR/article/view/17761.