<All ISBNs are 10 digits, newer books have 10 and 13 digit ISBNs>

Thank you for responding, but the reply wasn't helpful in answering my question. The question was "what does the X signify?"

<ISBN 0-13-929001-X>

The reason for asking is because apparently the patent holder questioned when the transputer reference manual was made public. (See first post on this thread) Now if you scan the other transputer references in the link below you will see most just have all numbers. A couple have an X after the ISBN number. I think from that listing one would assume that the X is signifying something different from the rest. Perhaps not connected to public distribution but, if it is, then the information is very telling.

ttp://wotug.ukc.ac.uk/parallel/bibliographies/transputer/books.bib

Can you comment further?

TIA, Opty