1. Qualitative Methods in Mathematical Analysis;El’sgol’c,1964
2. Introduction to the Theory andApplication of Differential Equations with Deviating Arguments;El’sgol’ts,1973
3. Oscillation Theory of Delay Differential Equations;Gyri,1991
4. Oscillation Theory for Functional Differential Equations;Erbe,1995
5. Functional Differential Equations;Hale,1977