1. L.È. Èl'sgol’ts, Introduction to the theory of differential equations with deviating arguments (translated from the Russian by Robert J. McLaughlin Holden-Day, Inc., San Francisco, California, 1966).
2. L.È. Èl'sgol’ts, S.B. Norkin, Introduction to the theory and application of differential equations with deviating arguments (translated from the Russian by John L. Casti. Mathematics in Science and Engineering, vol. 105, Academic Press, New York, 1973).
3. Theory of Functional Differential Equations;Hale,1977