I would like to go on record saying that ISBN numbers are utterly useless. Consider this:
* older books don't have ISBN numbers, * the hardcover and softcover version of the same book have completely unrelated ISBN numbers, * different editions of a book have completely unrelated ISBN numbers, * even different printings of one and the same edition get different ISBN numbers.
Because of this, it is impossible to reliably locate a book by ISBN in a library or bookstore. The system is broken by design. A much more rational way to code book references would be with the Library of Congress classification codes (which can be found inside the front cover of every book, right above the ISBN).
Axel