1. Differential Equations, Stability, Oscillations, and Time Lags;Halanay,1966
2. Behavior of Solutions of Functional Differential Equations near a Periodic Orbit;Hale,1968
3. Functional Differential Equations;Hale,1971
4. Periodic solutions of differential equations with time lag continuing a small parameter;Perello;J. Differential Equations,1968