Apart from a number of minor corrections and changes, a substantial reformulation and up-dating of Chapters 14 and 15 has taken place. This reformulation and up-dating is a major and very welcome contribution from my friend and colleague, Dr J.W. Sanders, to whom I express my sincere thanks. His efforts have produced a much better result than I could have achieved on my own. Warm thanks are also due to Dr Jo Ward, Who checked some of the revised material. New Sections 16.9 and 16.10 have also been added. The bibliography has been expanded and brought up to date, though it is still not exhaustive. In spite of these changes, the third paragraph in the Preface to the revised edition of Volume I is applicable here. What has been aeeomplished here is not a complete account of developments over the past 15 years; such an account would require many volumes. Even so, it may assist some readers who wish to appraise some of these developments. More ambitious readers should consult Mathematical Reviews from around Volume 50 onwards.

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