Nagl, Manfred, Gregor Engels, Rupert Gall, and Wilhelm Schäfer. “Software Specification by Graph Grammars.”https://doi.org/dx.doi.org/10.1007/BFb0000113__In Proceedings of the 2nd International Workshop on Graph-Grammars and Their Application to Computer Science, Osnabrück (Germany), 153:267–87. LNCS. Berlin/Heidelberg: Springer, 1983.https://doi.org/dx.doi.org/10.1007/BFb0000113 .
LibreCat: /record/8255
DOI: dx.doi.org/10.1007/BFb0000113

Engels, Gregor, Rupert Gall, Manfred Nagl, and Wilhelm Schäfer. “Software Specification Using Graph Grammars.”http://dx.doi.org/10.1007/BF02251236__Computing 31, no. 4 (1983): 317–46.http://dx.doi.org/10.1007/BF02251236 .
LibreCat: /record/7411
DOI: http://dx.doi.org/10.1007/BF02251236

Engels, Gregor, Udo Pletat, and Hans-Dietrich Ehrich. “An Operational Semantics for Specifications of Abstract Data Types with Error Handling.”http://dx.doi.org/10.1007/BF00265557__Acta Informatica 9, no. 3 (1983): 235–54.http://dx.doi.org/10.1007/BF00265557 .
LibreCat: /record/7412
DOI: http://dx.doi.org/10.1007/BF00265557

Engels, Gregor, and Wilhelm Schäfer. “Specification of a Programming Support Environment by Graph Grammars.” In Proceedings of the Conference on Graphtheoretic Concepts in Computer Science (WG), München (Germany), 47–62. München/Leipzig: Hanser, 1982.
LibreCat: /record/7811

Pletat, Udo, Gregor Engels, and Hans-Dietrich Ehrich. “An Operational Approach to Conditional Algebraic Specifications.” In Proceedings of the 7eme Colloque Sur Les Arbres En Algebre et En Programmation, Lille (France), 82:254–70, 1982.
LibreCat: /record/7812

Engels, Gregor, Udo Pletat, and Hans-Dietrich Ehrich. Handling Errors and Exceptions in the Algebraic Specifications of Data Types. University of Osnabrück, 1981.
LibreCat: /record/8184

Pletat, Udo, Gregor Engels, and Hans-Dietrich Ehrich. Operational Semantics of Algebraic Specifications with Conditional Equations. University of Dortmund, Department of Computer Science, 1981.
LibreCat: /record/8185