In this paper we use approximation methods to examine the singular discrete boundary value problem \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage{bbm} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\left\{ \begin{gathered} - \Delta ^2 u(k - 1) = g(k,u(k)) + h(k,u(k)),k \in [1,T] \hfill \\ u(0) = 0 = u(T + 1) \hfill \\ \end{gathered} \right.$$ \end{document} where our nonlinearity may be singular in its dependent variable and is allowed to change sign.
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