This book owes its existence to the Niels Bohr Institute’s and Nordita’s hospitable and nurturing environment, and the private, national and crossnational fundations that have supported the collaborators’ research over a span of several decades. P.C. thanks M.J. Feigenbaum of Rockefeller University; D. Ruelle of I.H.E.S., Bures-sur-Yvette; I. Procaccia of the Weizmann Institute; P. Hemmer of University of Trondheim; The Max-Planck Institut f ̈r Mathematik, Bonn; J. Lowenstein of New York University; Eduificio Celi, Milano; and Funda ̧a de Faca, Porto Seguro, for the hospitality during various stages of this work, and the Carlsberg Foundation and Glen P. Robinson for the support.