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This was an age before e-books. We all knew that the only way you can allow a book to survive in print in the long term is in paperback. The hardback has a certain life, and then it stops having that. It stops selling, and if you want the book to just stay around there has to be a paperback edition. So if there were not a paperback edition the book would eventually disappear from the shelves, and we would have lost the battle.

Source: www.teachingbooks.net
This was an age before e-books. We all knew that the only way you can allow a book to survive in print in the long term is in paperback. The hardback has a certain life, and then it stops having that. It stops selling,