1. R.P. Agarwal, On Multipoint Boundary Value Problems for Discrete Equations, J. Math. Anal. Appl., 96 (1983), 520–534.
2. R.P. Agarwal, On Boundary Value Problems of Second Order Discrete Systems, Appl. Anal., 20 (1985), 1–17.
3. R.P. Agarwal, Difference Equations and Inequalities, Marcel Dekker, New York, 1992.
4. J.V. Baxley, Existence Theorems for Nonlinear Second Order Boundary Value Problems, J. Differential Equations, 85 (1990), 125–150.
5. J. Blot, P. Cieutat and J. Mawhin, Almost-Periodic Oscillations of Monotone Second-Order Systems, Adv. Differential Equations, 2 (1997), 693–714.