I will not make you a long commentary on this book, I advise you to read that of Mr Philippe Vallin who best summarized the subject.
I would just like to confirm that this book is a gold mine in which we find a wealth of information about our beloved progressive rock, from infancy, by reviewing its evolution through the various decades until today .... This small time travel is nice my faith.
Seriously, I advise you to let you captivated by this enjoyable book to go, well written, which surely allow you to discover (like me) groups which you never knew existed, and then twenty euros for a book like this one c is frankly a bargain!