Is public domain possible?

[Jerry]

On this page ...
http://www.gnu.org/philosophy/categories.html

Under: "Public domain software" ...

Is this statement:

--- [ begin quote ] ---
Under the Berne Convention, which most countries have signed, anything
written down is automatically copyrighted. This includes programs.
Therefore, if you want a program you have written to be in the public
domain, you must take some legal steps to disclaim the copyright on
it; otherwise, the program is copyrighted.
--- [ end quote ] ---

So is it possible to write a program and state on the program (eg. in
the About box) that it is public domain and thereby make the program
public domain?