P. Echenique. (2007)cite arxiv:0705.1845
Comment: 53 pages, 18 figures, the figures are at a low resolution due to
arXiv restrictions, for high-res figures, go to http://www.pabloechenique.com.
N. Messai, M. Devignes, A. Napoli, and M. Sma\"ıl-Tabbone. Proceedings of the 13th International Conference on Conceptual Structures (ICCS 2005), volume 3596 of Lecture Notes in Computer Science, page 323-336. Springer, (2005)