1. 1. AUTEBERT J.-M., BEAUQUIER J., BOASSON L. and LATTEUX M., Very small families of algebraic nonrational languages, in: Formal Language Theory, Book, R. (ed.), Academic Press, London-New York, 1981.
2. 2. BOASSON L., Un critère de rationalité des langages algébriques, in: Automata, Languages and Programming, Nivat, M. (ed.), North-Holland Publ. Comp., Amsterdam, 1973.3684870263.68038
3. 3. BOASSON L., Private communication.
4. 4. HARRISON M. A., Introduction to formal language theory, Addison-Wesley, Reading, Mass., 1978.5263970411.68058
5. 5. SALOMAA A., Formal languages, Academic Press, London-New York, 1973.4387550262.68025