This book was conceived in the winter of 1970 when I heard that I was
getting a Sloan Fellowship and I thought I would take a year off to write a
book. It took a bit longer than that, but I have many good excuses.
I am grateful to the Sloan Foundation, the National Science Foundation and the University of California for their financial support-and to
the Mathematics Department at UCLA for the stimulating and pleasant
working environment that it provides.
One often sees in prefaces long lists of persons who have contributed to
the project in one way or another and I hope I will be forgiven for not
complying with tradition; in my case any reasonably complete list would
have to start with Lebesgue and increase the size of the book beyond the
publisher’s indulgence. I will, however, mention my student Chris Freiling
who read carefully through the entire final version of the manuscript and
corrected all my errors