1. A. M. Samoilenko, Elements of the Mathematical Theory of Multifrequency Oscillations [in Russian], Moscow, Nauka (1987).
2. A. M. Samoilenko and N. A. Perestyuk, Impulsive Differential Equations [in Russian], Vyshcha Shkola, Kiev (1987).
3. M. O. Perestyuk and P. V. Feketa, "Invariant manifolds of one class of systems of impulsive differential equations," Nelin. Kolyv., 13, No. 2, 240-252 (2010)
4. English translation : Nonlin. Oscillat., 13, No. 2, 260-273 (2010).
5. P. Feketa and Yu. Perestyuk, "Perturbation theorems for a multifrequency system with pulses," Nelin. Kolyv., 18, No. 2, 280-288 (2015)