PetryshynR. I. and PokhylaO. M. (1997) “Estimate of an error of the averaging method on a semiaxis for a multifrequency resonance system”, Ukrains’kyi Matematychnyi Zhurnal, 49(5), pp. 685–690. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/5049 (Accessed: 24November2024).