PREFACE TO THE FIRST EDITION xiii
Christoph Sorger, Joost van Hamel, and Weiqiang Wang, who made valuable sug-
gestions and pointed out various typos. We also thank Ralph Sizer of the AMS for
his sharp editorial work and Vladimir Prenkel for his careful drawing of the figures
appearing in this book.
Edward Prenkel wishes to thank Boris Feigin for his longtime collaboration,
and Alexander Beilinson and Vladimir Drinfeld for many illuminating discussions.
The authors gratefully acknowledge the support that they received in the course
of writing this book from the Packard Foundation and the NSF.