MitropolskiyY. A. and KhomaG. P. (1993) “On the periodic solutions of the second-order wave equations. V”, Ukrains’kyi Matematychnyi Zhurnal, 45(8), pp. 1115–1121. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/5908 (Accessed: 24November2024).