Giorgio Ausiello Mariangiola Dezani-Ciancaglini Simona Ronchi Della Rocca Automata, Languages and Programming, 16th International Colloquium, ICALP89, Stresa, Italy, July 11-15, 1989, Proceedings ICALP Lecture Notes in Computer Science 372 Springer 1989 3-540-51371-X db/conf/icalp/icalp89.html