G. Goguadze, E. Melis, C. Ullrich, and P. Cairns. Proceedings of Second International Conference on Mathematical Knowledge Management, MKM03, page 80--93. Springer-Verlag, (2003)
E. Melis, R. Shen, J. Siekmann, C. Ullrich, F. Yang, and P. Han. Proceedings of the 2005 Joint Chinese-German Workshop on Cognitive Systems, volume 4429 of Lecture Notes in Artificial Intelligence, page 36--44. Shanghai, China, Springer-Verlag, (2007)
C. Groß, M. Moormann, and C. Ullrich. DES-Time 2006, Proceedings of the International Symposium on Technology and its Integration into Mathematics Education 2006, Dresden, Germany, (July 2006)