Andrzej Lingas Rolf G. Karlsson Svante Carlsson Automata, Languages and Programming, 20nd International Colloquium, ICALP93, Lund, Sweden, July 5-9, 1993, Proceedings ICALP Lecture Notes in Computer Science 700 Springer 1993 3-540-56939-1 db/conf/icalp/icalp93.html