I hate to point this out, but I have through this discussion been made aware
of the Wikibooks:Copyright page, which was written by two very well known
non-lawyers. The purported copyright notice at the top of that very page
does not even identify by whom the supposed copyright is owned. This is not
a simple question, and I expect to have a closer look at the page line by
line in the future.
All I'm saying is, beware quoting the Wikibooks:Copyright page as sacred