1. G. Ladas, Ch. G. Philos, and Y. G. Sficas, “Sharp conditions for the oscillation of delay difference equations,” J. Appl. Math. Simulat., 2, No. 2, 101–111 (1989).
2. I. Györi and G. Ladas, Oscillation Theory of Delay Differential Equations with Applications, Oxford Math. Monogr., Clarendon Press, Oxford (1991).
3. G. E. Chatzarakis, R. Koplatadze, and I. P. Stavroulakis, “Optimal oscillation criteria for first order difference equations with delay argument,” Pacific J. Math.,235, No. 1, 15–33 (2008).
4. R. Koplatadze and S. Pinelas, "Oscillation criteria for the first-order linear difference equation with several delay arguments," Nelin. Kolyv.,17, No. 2, 248-267 (2014)
5. English translation: J. Math. Sci., 208, No. 5, 571-592 (2015).