D. Ignatov, and S. Kuznetsov. Proceedings of the 17th International Conference on Conceptual Structures (ICCS 2009), volume 5662 of Lecture Notes in Computer Science, page 185-200. Springer, (2009)
M. y Gómez, A. Gelbukh, and A. López-López. Proceedings of the 10th International Conference on Conceptual Structures (ICCS 2002), volume 2393 of Lecture Notes in Computer Science, page 122-136. Springer, (2002)