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2. A.M. Lyapunov, The General Problemof the Stability of Motion (ONTI, Moscow, 1935; Taylor & Francis, London, 1992).
3. I. G. Malkin, “A theorem on stability in the first approximation,” Dokl. Akad. Nauk SSSR 76(6), 783–784 (1951).
4. V. I. Zubov, Lyapunov Methods and Their Application (Vysshaya Shkola, Moscow, 1973) [in Russian].
5. G. V. Kamenkov, Selected Works, Vol. 1: Stability of Motion. Oscillations. Aerodynamics (Nauka, Moscow, 1971) [in Russian].