REFERENCES
- ANDRONOV A. A. WITT A. A. , 1933 , J. Exp. Theor. Physics , 3 ( 5 ) (in Russian).
- ANDRONOV , A. A. , WITT , A. A. and HAIKIN , S. E. 1981 . Oscillation Theory , 468 Moscow : Nauka . in Russian
- BUTENIN , N. V. , NIEMARK , YU. , I. and FUFAEV , N. A. 1976 . Introduction to the Theory of Nonlinear Oscillations , 384 Moscow : Nauka . in Russian
- DEMIDOVICH , B. P. 1967 . Lectures on the Mathematical Theory of Stability , 472 Moscow : Nauka . in Russian
- MIL'MAN V. D. MYSHKIS A. D. , 1960 , Siberian Math. J. , 1 , 233 (in Russian).
- MYSHKIS A. D. SAMOILENKO A. M. , 1967 , Mathematicheskij Sbornik , 74 , 202 (in Russian).
- SAMOILENKO A. M. PERESTIUK N. A. , 1977 , Differencial'nye Uravn. , 11 , 1981 (in Russian); 1981, Ibid., 11, 1995 (in Russian) .
- SIMEONOV P. S. BAINOV D. D. , 1983 , Systems Control Lett. , 3 , 297 ; 1985 a, J. math. Analysis Applic., 109, 546; 1985 b, Tamkang J. Math., 16, 19; 1986 a, COMPEL, 5, 95; 1986 b, J. math. Analysis Applic., 117, 247 .