Hartmut Ehrig, Hans-Jörg Kreowski, Andrea Maggiolo-Schettini, Barry K. Rosen, Jozef Winkowski: Transformations of Structures: An Algebraic Approach. Math. Systems Theory 14:305-334, 1981.
Hans-Jörg Kreowski: A Comparision Between Petri-Nets and Graph Grammars. In Proc. Workshop WG'80 on Graphtheoretic Concepts in Computer Science (Bad Honnef, June 1980), volume 100 of Lecture Notes in Computer Science, pages 306-317. Springer, 1981.
Hans-Jörg Kreowski: Algebraische Spezifikation von Softwaresystemen. In Proc. GACM-Konferenz Software Engineering - Entwurf und Spezifikation (Berlin, Sept. 1980), volume 5 of Berichte des German Chapter of the ACM, pages 46-74. Teubner, Stuttgart, 1981.
Hartmut Ehrig, Werner Fey, Hans-Jörg Kreowski: Algebraische Spezifikation eines Stücklistensystems - eine Fallstudie. In Proc. GACM-Konferenz Software Engineering - Entwurf und Spezifikation (Berlin, Sept. 1980), volume 5 of Berichte des German Chapter of the ACM, pages 75-90. Teubner, Stuttgart, 1981.
Hans-Jörg Kreowski, Grzegorz Rozenberg: On the Constructive Description of Graph Languages Accepted by Finite Automata. In Proc. Conference MFCS'81 (Strbske Pleso, Aug./Sept. 1981), volume 118 of Lecture Notes in Computer Science, pages 398-409. Springer, 1981.
