R. Bellman and K. L. Cooke, Differential-Difference Equations, Academic Press, New York (1963).
J. Hale, Theory of Functional Differential Equations, Springer, New York (1977).
A. M. Samoilenko and G. P. Pelyukh, “Solutions of systems of nonlinear functional differential equations bounded on the entire real axis and their properties,” Ukr. Mat. Zh., 46, No. 6, 737–747 (1994).
H. P. Pelyukh, “Asymptotic properties of solutions of systems of nonlinear functional differential equations with nonlinear deviation of argument,” in: Proceedings of the Ukrainian Mathematical Congress-2001 “Differential Equations and Nonlinear Oscillations” [in Ukrainian], Kyiv (2002), pp. 94–100.
G. P. Pelyukh, “On asymptotic properties of solutions of nonlinear functional differential equations,” Differents. Uravn., 39, No. 1, 45–49 (2003).
G. P. Pelyukh, “On the structure of the set of solutions of one class of systems of nonlinear functional differential equations of neutral type,” Nelin. Kolyvannya, 5, No. 1, 58–65 (2002).