Ronto N. I. and Martynyuk O. M. (1992) “Study of periodic solutions of the second-order notations”, Ukrains’kyi Matematychnyi Zhurnal, 44(1), pp. 83-93. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/7798 (Accessed: 24November2024).