copyright of gnuchess book

Hi all,

What's the exact copyright info of GNU Chess openings book
(book_1.01.pgn.gz)? I found a note in the Debian package distribution
stating that this package is in the public domain, is this correct?

I would be grateful if someone could post the detailed copyright info of
this package, so that I could give credits to its creators when
redistributing this package.

Thanks,

Alex