In the two years since the first edition of this book was published I’ve
received numerous messages from readers all around the world. I
was surprised by this large number of responses and how positive
most of them were. Of course, I was cautiously confident that read-
ers would like the book. Otherwise I wouldn’t have spent so many
months writing it. However, there is certainly no shortage of books
on group theory or on the role of symmetries in physics. To quote
Predrag Cvitanovic
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