Yves Bertot is a Senior Researcher and Project Leader at the French National Institute for Research in Computer Science and Control (INRIA), Sophia Antipolis. Born in 1964, he received his Ph.D. from the University of Nice in 1991 and is co-author (with Pierre Castéran) of Coq'Art: The Calculus of Inductive Constructions (2004). Gérard Huet is a Director of Research at the French National Institute for Research in Computer Science and Control (INRIA), Rocquencourt. Jean-Jacques Lévy is a Director of Research at the French National Institute for Research in Computer Science and Control (INRIA), Rocquencourt. Gordon Plotkin is a Professor in the School of Informatics at the University of Edinburgh.