where a, c : Z ® R+ are T-periodic functions, f Î C(Z × (0, ∞), R) is T-periodic with respect to t and singular at u = 0. Positive periodic solutions of second-order difference equations have been studied by many authors, see [1-6]. However, in these therein, the nonlinearities are nonsingular, what would happen if the nonlinearity term is singular? It is of interest to note here that singular ...