1. N. N. Bogolyubov and Yu. A. Mitropolsky, Asymptotic Methods in the Theory of Nonlinear Oscillations [in Russian], Fizmatlit, Moscow (1958).
2. L. N. Bulaevskii and A. E. Koshelev, “Radiation due to Josephson oscillations in layered superconductors,” Phys. Rev. Lett., 99, 057002 (2007).
3. E. I. Butikov, “An improved criterion for Kapitzas pendulum stability,” J. Phys. A: Math. Theor., 44, 295202 (2011).
4. B. V. Chirikov, Nonlinear Resonance [in Russian], Novosibirsk (1977).
5. S. G. Glebov, O. M. Kiselev, and N. Tarkhanov, Nonlinear Equations with Small Parameter, De Gruyter, Berlin–New York (2017).