B. Ganter, P. Grigoriev, S. Kuznetsov, and M. Samokhin. Proceedings of the 12th International Conference on Conceptual Structures (ICCS 2004), volume 3127 of Lecture Notes in Computer Science, page 94-108. Springer, (2004)
H. Kim, S. Hwang, and H. Kim. SAC '07: Proceedings of the 2007 ACM symposium on Applied computing, page 1340--1345. New York, NY, USA, ACM Press, (2007)