Jean-Claude Falmagne is emeritus professor of cognitive sciences at the Universtiy of California, Irvine. His research spans topics in psychophysics, probabilistic choice theory, combinatorics, measurement theory, educational technology, and philosophy of science.Jean-Paul Doignon is a professor of the mathematics department of the Universit� Libre de Bruxelles, Belgium. His research covers various aspects of discrete mathematics (graphs, ordered sets, convex polytopes, etc.) and applications to behavioral sciences (preference modelling, choice models, knowledge assessment, etc.).