Footnotes have been collected and repositioned just before the Index.
Some in-line paragraph headings are in boldface and some are in italics; this emphasis has been retained.
Index not checked for proper alphabetization or correct page references, but to page 274 was a typographical error and has been changed to 174.
Page [155]: Text refers to c c′ in [Figs. 38–39], but neither figure appears to contain a c′ label.