1. N.G. Chetaev, Stability of Motion, Nauka, 1990. In Russian.
2. I.G. Malkin, Theory of Stability of Motion, Nauka, 1966. In Russian.
3. N.N. Krasovsky, Some problems in the theory of stability of motion, Fizmatgiz, 1959. In Russian.
4. On Liapounoff's Conditions of Stability
5. V.M. Matrosov, Trudy of Kazan Aviation Institute 45, 63–76 (1959). In Russian.