1. Berstel, J., Perrin, D., Reutenauer, C.: Codes and Automata. Cambridge University Press, Cambridge (2009)
2. Eilenberg, S.: Automata, Languages, and Machines, vol. B. Academic Press, New York, 1976 [Harcourt Brace Jovanovich Publishers], With two chapters (“Depth decomposition theorem” and “Complexity of semigroups and morphisms”) by Bret Tilson, Pure and Applied Mathematics, vol. 59
3. Froidure, V., Pin, J.-E.: Algorithms for computing finite semigroups. In: Foundations of Computational Mathematics, Rio de Janeiro, 1997, pp. 112–126. Springer, Berlin (1997)
4. Lallement, G.: Semigroups and Combinatorial Applications. Wiley, New York (1979). Pure and Applied Mathematics, a Wiley-Interscience publication
5. Schützenberger, M.-P.: On the synchronizing properties of certain prefix codes. Inf. Control 7, 23–36 (1964)