At various stages during the writing of this book I have been enormously helped by encouragement, advice, and detailed (but always constructive!) criticism, from a number of people, including Stuart Andrews, Roger Ashley, Michael Cansdale, James John, Gareth Jones, William Keyser, Bill White, and my editor at Icon, Duncan Heath. Tim Wood, of St Andrews Press, Kate Noble, and Chris Lee have kindly helped me with diagrams and design. All errors are of course my own responsibility.