1. M.P. Chen, B.G. Zhang. Oscillation and Comparison Theorems of Difference Equations with Positive and Negative Coefficients.Bull. Math. Inst. Academia Sinica., 1994, 22: 295–306
2. G. Zhang, S.S. Cheng. Oscillation Criteria of a Neutral Difference Equation with Delay.Appl. Math. Lett., 1995, 8: 13–17
3. I. Gyori, G. Ladsa. Oscillation Theory of Delay Differential Equations with Applications. Oxford University Press, Oxford, 1991
4. G. Ladas. Oscillation of Difference Equations with Positive and Negative Coeffcients.Rocky Mountain J. Math., 1990, 20: 1051–1061
5. Q. Chuanxi, G. Ladas. Oscillatory Behavior of Difference Equations with Positive and Negative Coefficients.Le Math., 1989, XLIV: 293–309