1. Berstel, J., Boasson, L.: Formal properties of XML grammars and languages. Acta Informatica 38, 649–671 (2002)
2. Berstel, J.: Transductions and Context-Free Languages. Teubner, Stuttgart (1979)
3. Brüggemann-Klein, A., Wood, D., Murata, M.: Regular tree and regular hedge languages over unranked alphabets: Version 1. unfinished technical report (April 2001), http://citeseer.ist.psu.edu/451005.html
4. Comon, H., Dauchet, M., Gilleron, R., Jacquemard, F., Lugiez, D., Tison, S., Tommasi, M.: Tree Automata Techniques and Applications. Unpublished electronic book (1997), http://www.grappa.univ-lille3.fr/tata
5. Eilenberg, S.: Automata, languages, and machines, vol. A. Academic Press, London (1974)