Bernard ROY Professor, University of Paris-Dauphine Director of LAMSADE 11 is not unusual for a dozen or so loosely related working papers to be published in book form as the natural outgrowth of a scientific gathering. Although many a volu- me of collected papers has come into point in this way, the homogeneity of the arti- cles included will often be more apparent than real. As the reader will quickly ob- serve, such is not the case with the present...