1. The direct method of Liapunov in stability of elastic systems;Movchan;Prik. Mat. Meh.,1959
2. Methods of A. M. Liapunov and Their Application;Zubov,1964
3. Stability of motion in the large;Barbashin;Dokl. Akad. Nauk SSSR,1952
4. Asymptotic stability criteria;LaSalle,1962
5. An invariance principle in the theory of stability;LaSalle,1967