1. Systems d’equations differentielle d’oscillations nonlineaires;Barbalat;Rev. Roumaine Math. Pures Appl.,1959
2. Nonlinear Functional Analysis;Deimling,1985
3. Coincidence Degree and Nonlinear Differential Equations;Gaines,1977
4. Stability and Oscillations in Delay Differential Equations of Population Dynamics;Gopalsamy,1992
5. Environmental periodicity and time delays in a “food-limited” population model;Gopalsamy;J. Math. Anal. Appl.,1990