Developments in Language Theory 5th International Conference, DLT 2001, Vienna, Austria, July 16-21, 2001. Revised Papers - Kuich, Werner; Kuich, Werner; Rozenberg, Grzegorz; Rozenberg, Grzegorz; Salomaa, Arto; Salomaa, Arto (Springer Berlin Heidelberg : Imprint: Springer, 2002)