1. Ch. Babbage, ‘‘An essay towards the calculus of functions, Part II,’’ Philos. Trans. R. Soc. London 106, 179–256 (1816).
2. W. B. Fite, ‘‘Properties of the solution of certain functional differential equations,’’ Trans. Am. Math. Soc., No. 3, 311–319 (1921).
3. T. Carleman, ‘‘Sur la theorie des equations integrales et ses applications,’’ in Proceedings of the International Mathematical Congress (Zurich, 1932), Vol. 1, pp. 138–151.
4. Chap. 8;S. F. Lacroix,1819
5. N. K. Karapetyants and S. G. Samko, Equations with Involutive Operators (Birkhäuser, Boston, MA, 2001).