1. A. Aho, J. Hopcroft, J. Ulman, The Design and Analisys of Computer Algorithms, Addison-Wesley, 1974.
2. J. Almeida, Implicit operations on finite J-trivial semigroups and a conjecture of I. Simon, J. Pure Appl. Alg., 69(1990), 205–208.
3. M.-P. Beal, J. Senellart, On the bound of the synchronization delay of local automata, Theoret. Comput. Sci. 205, 1-2(1998), 297–306.
4. Lect. Notes in Comp. Sci;D. Beauquier,1989
5. D. Beauquier, J.E. Pin, Languages and scanners, Theoret. Comp. Sci, 1, 84(1991), 3–21.