Hartmut Ehrig, Hans-Jörg Kreowski: Systematic Approach of Reduction and Minimization in Automata and Systems Theory. Computer Systems Science 12:269-304, 1976.
Hartmut Ehrig, Hans-Jörg Kreowski: Parallel Graph Grammars. In Aristid Lindenmayer, Grzegorz Rozenberg, editors, Proc. Automata, Languages, Development, pages 425-442. North-Holland, Amsterdam, 1976.
Hartmut Ehrig, Hans-Jörg Kreowski: Categorial Approach to Graphic Systems and Graph Grammars. In Proc. Algebraic System Theory (Udine, 1975), volume 131 of Lecture Notes in Econ. Math. Systems, pages 323-351. Springer, 1976.
Hartmut Ehrig, Hans-Jörg Kreowski: Minimization Concepts of Automata in Pseudoclosed Categories. In Proc. Algebraic System Theory (Udine, 1975), volume 131 of Lecture Notes in Econ. Math. Systems, pages 359-374. Springer, 1976.
Hartmut Ehrig, Hans-Jörg Kreowski: Parallelism of Manipulations in Multidimensional Information Structures. In Proc. Conference Math. Foundations of Computer Science (Gdansk), volume 45 of Lecture Notes in Computer Science, pages 284-293. Springer, 1976.
