From the reviews of the first printing of this book, published as volume 6 of the Encyclopaedia of Mathematical Sciences: "... My general impression is of a particularly nice book, with a well-balanced bibliography, recommended!"

Medelingen van Het Wiskundig Genootschap, 1995

"... The authors offer here an up to date guide to the topic and its main applications, including a number of new results. It is very convenient for the reader, a carefully prepared and extensive bibliography ... makes it easy to find the necessary details when needed. The books (EMS 6 and EMS 39) describe a lot of interesting topics. ... Both volumes are a very valuable addition to the library of any mathematician or physicist interested in modern mathematical analysis."

European Mathematical Society Newsletter, 1994

"...The authors are recognized experts in their fields and so are ideal choices to write such a survey. ...The text of the book is liberally sprinkled with illustrative examples and so the style is not heavy going or turgid... The bibliography is very good and extremely large ..."

IMS Bulletin, 1995