Oscillations of Delay Difference Equations with Oscillating Coefficients

In this paper we establish sufficient conditions for the oscillation of all solutions of the delay difference equation yn + 1 − yn + pnyn − k = 0, n = 0, 1, 2, ..., where {pn} is a sequence of real numbers and k is a positive integer. An open problem in Ladas (in "International Conference on Differential Equations, Stability and Control," Dekker, New York, 1990) is solved.