1. V. S. Andreev, Nonlinear Electrical Circuit Theory [in Russian], Svyaz', Moscow (1972).
2. F. I. Barsukov, Generation and Selection of Low-Frequency Signals [in Russian], Énergiya, Moscow (1968).
3. N. N. Bogolyubov and Yu. A. Mitropol'skii, Asymptotic Methods in the Theory of Nonlinear Oscillations [in Russian], Nauka, Moscow (1974).
4. G. S. Veksler and Ya. I. Tetel'baum, Power Supply of Radio Equipment [in Russian], Tekhnika, Kiev (1966).
5. V. O. Kononenko, Vibrating Systems with a Limited Power Supply, Iliffe Books Ltd., London (1969).