... received a lot of assistancealong the way. Parts of this book were first presented in a pubescent stageto a seminar I presented at Indiana University in 198 1-82. In the sem-inar were Greg Adams, ... who read severalchapters. Here Paul McGuire, Bill Ross, and Liming Yang were of greathelp. Finally, special thanks go to David Minda for a very careful read-ing of several chapters with many ... means that there is a subset Xof80 such that OD \ Xhasmeaaureoandf' (a) existsfurallainX;alternately,f'(o)existsforalmost every a in 80. The words "almost everywhere" are abbreviated...