"The author has not been loath to publish his ongoing work nor to present it in systematic lectures and courses, and the volume under review could be regarded as a compendium of work that has already appeared in print. However, both in its integration of the work and the simplifications afforded by steady research in the subject, the book is pleasingly accessible, satisfying self-contained, and magisterial in presentation. [...] This volume is enticing in its elegance and simplicity at first and inveigles the reader to get involved in some of its later complexities." Mathematical Reviews