reading—and numerous corrections—of nearly the entire manuscript. Of
course any errors that remain are my own doing. I have appreciated TeXni-
cal rescues from Caroline Johnson, Barbara Beeton, and Richard Spjut.
Natalya Pluzhnikov's perceptive and thorough copy editing helped me put
the manuscript in final form. And I thank editor Ina Mette of the AMS for
her patience and encouragement, and for her thoughtful selection of excellent
Finally, I thank my dear family for the inspiration, love, and encourage-
ment that have sustained me throughout my work on this project.