Acknowledgements
This book started life many years ago as an occasional series of talks to various different audiences, including students at City University, fellow researchers at Microsoft Research Cambridge, and academics at Girton College, Cambridge. Questions and comments from these audiences were immensely helpful.
My wife Georgina, and my son Colin, have both read drafts of this book at different stages and given me a lot of very useful feedback. Michael Williams and another reviewer for Open Book Publishers did the same. Alessandra and the team at Open Book have been unfailingly helpful. Colin also contributed to the design of the cover.
The bibliography at the end lists some books that have given me food for thought. But as indicated there, my primary source for many areas with which I was unfamiliar before researching this book has been Wikipedia. So I would particularly like to thank the huge number of anonymous authors of Wikipedia articles on whose work and insights I have relied.
The mistakes are of course my own.
Stephen Robertson
Norfolk, 2020