Public domain software is not open-source?

[Rick Moen]

Quoting Matthew Flaschen (matthew.flaschen at gatech.edu):

> 
> Public domain is certainly not a license, so it can't be an approved 
> open source license.

"Objection, your honour.  Lacks foundation."

I.e., your discussion assumes software that actually _is_ in the public
domain, but which software are you speaking of -- and isn't the question
of whether it's really public domain or not the very thing that must
first be determined?  

See:  "Public Domain" on http://linuxmafia.com/kb/Licensing_and_Law/ ,
for my recap of some obstacles to unambiguously nullifying, by act of
will, a work's copyright ownership interest, before expiration of its
copyright term.