My identifiers are
[1] 0-671-65831-x
[1] 0-671-73593-4
[1] 978-0-671-74715-2
[1] goodreads
[5640] isbn
I understand the last two identifiers, but I have no idea where the first 3 number identifiers originate. They are obviously associated with single books, but I fail to find the number in the metadata or the book.
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