single book, search results

The 13-digit ISBN can start with 978 <b>or 979</b>, which will then in the second case not be covered by any 10-digit ISBN, e.g. www.amazon.com/dp/B0065GAW9M/ , cf. https://en.wikipedia.org/wiki/List_of_ISBN_identifier_groups#Identifiers_of_the_979-_prefix . This still seems to be a very rare case, but I think we should prefer 13-digit over 10-digit ISBN.