The following material is excepted from this:
1. The material from the "1984 CDC6000 Pascal compiler", which carries its own rights agreement from the University of Minnesota. The rights for this material are according to the agreement, which is included on this website conspicuously at the top of the material.
In the United States, the term and concept of "public domain" explicitly appeared in the law governing copyright. Specifically, it stated that a work would fall into the public domain unless specifically copyrighted.
With the adoption of the Berne Convention, an international treaty, the United States copyrights became governed by the Berne convention copyright laws known as "Berne Convention for the Protection of Literary and Artistic Works". In short, it specifies that copyright is automatic, and it may not be required to specifically attach a copyright to the work for it to be subject to such "automatic copyright".
I, as I am sure many others, believe the omission of the public domain from the official language of the copyright law is a mistake. Public domain works are a tradition that goes back centuries. Public domain serves an important purpose of freely disseminating knowledge. There are many reasons why a work would be given to the public domain, not all of them non-commercial.
In any case, I don't think that the public domain is dissolved with the Berne convention. The first proof of this is that the Berne Convention text (which you can read above) specifically mentions "public domain", even if it does not define it. The second proof of this is that the Berne Convention text itself is freely distributed without claims of rights of any kind. The Berne Convention text itself is public domain. It constitutes both an example of a public domain work, and also of why the public domain exists, since it would hardly do to publish a law on what rights of distribution are, which is itself restricted in publication!
Further, there is no precedence for a work that was specifically committed to the public domain, which was then later removed from the public domain and copyrighted. Any disputes have centered around the concept of what it means to "commit to the public domain", which was never codified by law, either by Berne Convention, or previous United States copyright laws.
I assert here the opinion that specifically stating that I release the works on this website from any rights, and commit it to the public domain, qualifies as defacto proof that the works are, in fact, in the public domain. I am not a lawyer, but I don't believe there is any possibility that one could claim that a work, once committed to the public domain, could be then claimed as under copyright.