Mitropolsky, Yu. A. “Construction of Asymptotic in Krylov-Bogoliubov-Mitropolsky Sense Solution of Wave Equations”. Vietnam Journal of Mechanics 29, no. 3 (September 22, 2007): 221–243. Accessed May 7, 2024. https://vjs.ac.vn/index.php/vjmech/article/view/5534.