- Juhani Karhumäki, Hermann A. Maurer, Gheorghe Paun, Grzegorz Rozenberg, editors, Jewels are Forever, Contributions on Theoretical Computer Science in Honor of Arto Salomaa. Springer, 1999.
- Ernst-Rüdiger Olderog, Bernhard Steffen, editors, Correct System Design, Recent Insight and Advances, (to Hans Langmaack on the occasion of his retirement from his professorship at the University of Kiel). Volume 1710 of Lecture Notes in Computer Science, Springer, 1999.