David Makinson King's College, London Title: Propositional relevance through letter-sharing Abstract: The concept of relevance between classical propositional formulae, defined in terms of letter-sharing, has been around for a very long time. But it began to take on a fresh life in 1999 when it was reconsidered in the context of the logic of belief change. Two new ideas appeared in independent work of Odinaldo Rodrigues and Rohit Parikh. First, the relation of relevance was considered modulo the belief set under consideration, Second, the belief set was put in a canonical form, known as its finest splitting. In this paper we explain these ideas; relate the approaches of Rodrigues and Parikh to each other; and briefly report some recent results of Kourousias and Makinson on the extent to which AGM belief change operations respect relevance. Finally we suggest a further refinement of the notion of relevance by introducing a parameter that allows one to take epistemic as well as purely logical components into account. ============================================================== Brief Biodata: David (Clement) Makinson received his B.A. (First class honours) from Sydney University in 1961, and D.Phil. from Oxford University in 1965. During 1965-1980 he was Professor at the American University of Beirut, Lebanon. During 1980-2001 he was Programme Specialist in the Division of Social Science Research and Policy (SHS/SRP), Sector of Social and Human Sciences, UNESCO, Paris. During this period he was also the Editor-in-Chief of UNESCO's International Social Science Journal. Currently he is a Senior Research Fellow in Unit of Logic Language and Computation, Department of Computer Science, King's College London. David Makinson (along with Peter Gardenfors and Carlos Alchourron) is one of the three founding fathers of the area of Theory Change (known as the AGM system). His current research areas include nonmonotonic logics, input/output logics, logic of norms, and logic of belief change. Author of two books in logic ("Topics in modern logic", Methuen, 1973 - in three languages - and "Bridges From Classical To Nonmonotonic Logic", King's College Publications, 2005), he has published over fifty frequently cited papers that appeared in leading international journals including J. Artificial Intelligence, J. Logic and Computation, Logic Journal of the IGPL, J. Logic, Language and Information, J. Philosophical Logic, Studia Logica, J. Symbolic Logic, Zeitschrift Math. Logik and Theoria. Webpage: http//www.dcs.kcl.ac.uk/staff/makinson/