1. Theory of Oscillations;Andronov,1949
2. Asymptotic Methods in the Theory of Non-Linear Oscillations;Bogoliubov,1961
3. Qualitative integration of a system of n differential equations in a region containing a singular point and a limit cycle;Brushinskaya;Dokl. Akad. Nauk. SSSR,1961
4. The bifurcation of one or more closed orbits from an equilibrium point of an autonomous differential system;Chafee;J. Differential Equations,1968
5. Differential Equations: Stability, Oscillations, Time Lags;Halanay,1966