1. R. P. Agarwal, “Difference equations and inequalities,” Marcel Dekker, New York, 2000.
2. Discrete Oscillation Theory
3. R. Arul and G. Ayyappan, “Oscillation theorems for second order neutral delay and advanced difference equations,” Inter. J. Diff. Eqn. Appl. 12, 13–25 (2013).
4. L. E. Elsgolts and S. B. Norkin, “Introduction to the theory and applictions of differential equations with deviating arguments,” Academic Press, New York, 1973.
5. I. Gyori and G. Ladas, “Oscillation theory of delay differnetial equations with applications,” Clarendan Press, Oxford, 1991.