Pierpaolo Degano Roberto Gorrieri Alberto Marchetti-Spaccamela Automata, Languages and Programming, 24th International Colloquium, ICALP'97, Bologna, Italy, 7-11 July 1997, Proceedings ICALP Lecture Notes in Computer Science 1256 Springer 1997 3-540-63165-8 db/conf/icalp/icalp97.html