L. Schröder, T. Mossakowski, and A. Tarlecki. International Colloquium on Automata, Languages and Programming (ICALP 2001), volume 2076 of Lecture Notes in Computer Science, page 993-1004. Springer; Berlin; http://www.springer.de, (2001)
B. Klin, P. Hoffman, A. Tarlecki, L. Schröder, and T. Mossakowski. Mathematical Foundations of Computer Science, volume 2136 of Lecture Notes in Computer Science, page 512--523. Springer; Berlin; http://www.springer.de, (2001)