[1]Agarwal R P. Difference Equations and  Inequalities.New York: Dekker,1992

[2]Erbe L H,Zhang  B G. Oscillation of discrete analogue of delay equations. Differential Integral Equations, 1989, 2:  300-309

[3]Ladas  G,Philos Ch G,Sficas Y G. Sharp condition for the oscillation of delay difference equation. J Appl Math Simulation, 1989, 2: 101-112

[4]Ladas G. Explicit condition for the oscillation of difference equations.J Math Anal Appl, 1990,153: 276-286

[5]Tang X H.Oscillation of delay difference equation with variable coefficients. J Central South Univ Tech, 1998,29(3): 287-288

[6]Tang X H,Yu J S. Oscillation of delay differnce equations.Comput Math Appl, 1999, 37: 11-20

[7]Tang X H,Yu J S. A further result on the oscillation of delay difference equations. Applieds Math Applic, 1999, 38: 229-237

[8]Tang X H, Yu J S. Oscillation of delay difference equations in a critical state. Applied Math Letters, 2000, 13: 9-15

[9]Tang X H, Yu J S. Oscillation of nonlinear delay difference equations. J Math Anal Appl, 2000, 249: 476-490

[10]Yu J S, Zhang B G,Qian  X Z. Oscillations of delay difference equations with deviating coefficients. J Math Anal Appl, 1993, 177: 423-444