1. A. M. Lyapunov,Problème Général de la Stabilité du Mouvement. Annals of Math. Studies, No. 17, Princeton Univ. Press, Princeton, N. J., 1947.
2. Wolfgang Hahn,Theory and Application of Liapunov's Direct Method, Prentice Hall, Englewood Cliffs, N. J., 1963.
3. Annals of Math. Studies;H. A. Antosiewicz,1958
4. T. Yoshizawa, Liapunov's function and boundedness of solutions,Funkcial. Ekvac. 2 (1959), 95–142.
5. N. N. Krasovskii,Stability of Motion. Applications of Lyapunov's Second Method to Differential Systems and Equations with Delay. Stanford Univ. Press, Stanford, Calif. 1963.