The present book is the first devoted to an extensive study of the algebraic structure of sS and the many applications thereof; it is an exciting book, written - and very well written - by two mathematicians who are eminently qualified two write it, and it is essentially self-contained, requiring only that the reader come to it with the basic concepts of first graduate courses in algebra, analysis and topology. I recommend this book highly; it will be very useful, both to researchers and to students. Its index, list of symbols and up-to-date bibliography are very helpful. Paul Milnes, Zentralblatt MATH / 1998 The authors present a self-contained exposition. The book under review is written by two mathematicians who have contributed in a decisive way to this rapidly expanding area and provides a unique opportunity to obtain a 'colorful' panoramic view of the subject. Michael Tkacenko, MathSciNet / 1999