[1]Haddock J R,Nkashama M N.Periodic boundary value problems and monotone iterative methods for functional differential equations.Nonlinear Anal,1994,22: 267-276

[2]Jiang D,Wei J. Monotone method for first and second order periodic boundary value problems and periodic solutions of functional differential equations.
Nonlinear Analysis,2002,50: 885-898

[3]Nieto J J, Jiang Y,Yan J R. Monotone iterative method for functional differential equations.Nonlinear Anal,1998,32: 741-747

[4]Nieto J J,  Rodrguez Lopez R. Existence and approximation of s olutions for nonlinear functionaldifferentialequations with periodic boundary value conditions. Comput Math Appl, 2000,40: 433-442

[5]Ladde G S,Lakshmikantham V,Vatsala A S.Monotone Iterative Techniques for Nonlinear Differential Equations.London Pitman Advanced Publishing Program,1985

[6]Leela S, Oguztoreli M N.Periodic boundary value problems for differential equations with delay and monotone iterative methods.J Math Anal Appl,1987, 122: 301-307

[7]Liz E,Nieto J J. Periodic boundary value problems for a cla ss of functional differential equations. J Math Anal Appl, 1996,200: 680-686

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

[9]Cabada A,Otero Espinar V. Optimal existence results for nth order periodic boundary value difference equations.J Math  Anal Appl,2000,247: 67-86

[10]Lakshmikantham V, Trigante D.Theory of Difference Equations: Nummerical Methods and  Applications.Mathematics in Science and Engineering.Bostan Academic Press,1988

[11]Zhuang W,  Chen Y, Cheng  S S. Monotone methods for a discrete boundary value problems.Comput Math  Appl,1996,  32: 41-49

[12]Pang Y H, Agarwal R P.  Periodic boundary value problems for first and s econd order discrete systems. Mathl Comput Modelling,1992, 16: 101-112

[13]Pang Y H, Agarwal R P. Monotone iterative methods for  a general class of discrete boundary value problems.Computers Math Applic, 1994, 28: 243-254

[14]Wang Y M. Monotone methods for a boundary value problem of second discrete equations. Computers Math Applic,1998, 36: 77-92

[15]Wang Y M. Monotone enclosure for a class of discrete boundary  value problems without monotone nonlinearities.Computers Math Applic,1998, 35: 51-60

[16]Wang Y M, Agarwal  R P. Remarks on periodic boundary value problems of first order discrete systems. Intern J Computer Math, 2000, 73: 493-502