Jean-Pierre Barthélemy et le principe de Pareto

After his first works in "pure" category theory, Jean-Pierre Barthelemy turns to completely different research directions, namely to discrete mathematics, computer sciences and their contributions to some problems of human or social sciences. His first work in these new areas deals with metric aggregation rules and the Pareto principle in consensus theory. I present this work and I mention developments done by Jean-Pierre Barthelemy himself and by other authors.