1. An Introduction to Difference Equations;Elaydi,2005
2. Difference Equations and Inequalities;Agarwal,1992
3. Oscillation Theory for Difference and Functional Differential Equations;Agarwal,2000
4. Oscillation Theory of Delay Differential Equations with Applications;Gyri,1991
5. Difference Equations, Theory and Applications;Mickens,1990