1. B. V. Bulgakov, “On Accumulation of Perturbations in Linear Oscillating Systems with Constant Parameters,” Dokl. Akad. Nauk SSSR 51(5), (1946).
2. V. V. Aleksandrov and V. N. Zhermolenko, “On Absolute Stability of Second-Order Systems,” Vestn. Mosk. Gos. Univ., Ser. 1, Mat. Mekh., No. 5, (1972).
3. V. N. Zhermolenko, “On the B. V. Bulgakov Problem on Maximum Deviation of a Second-Order Oscillating System,” Vestn. Mosk. Gos. Univ., Ser. 1, Mat. Mekh., No. 2, (1980).
4. O. V. Aleksandrova, “Generalized Resonance in an Oscillating System,” Vestn. Mosk. Gos. Univ., Ser. 1, Mat. Mekh., No. 3, (1991).
5. E. K. Lavrovskii and A. M. Formal’skii, “Optimal Control for Swinging and Deceleration of a Swing,” Prikl. Mat. Mekh. 57(2) (1993).