B. Ganter, and S. Kuznetsov. Proceedings of the 9th International Conference on Conceptual Structures (ICCS 2001), volume 2120 of Lecture Notes in Computer Science, page 129-142. Springer, (2001)
H. Pfeiffer, and R. Hartley. Proceedings of the 15th International Conference on Conceptual Structures (ICCS 2007), volume 4604 of Lecture Notes in Artificial Intelligence, page 165-178. Berlin, Heidelberg, Springer-Verlag, (July 2007)