1. Theory of Codes;Berstel,1985
2. Power Absorbing Languages and Semigroups, Words, Languages and Combinatorics II;Head,1994
3. Linear Algebra;Hoffman,1971
4. J.E. Hopcroft, J.D. Ullman, Introduction to Automata Theory, Languages and Computation, Addison-Wesley, Reading, MA, 1979.
5. Some properties of overlapping order and related languages Soochow;Hsu;J. Math.,1989