I'm writing an application for which I want to use some 20-year old open source code. The original code is kind of antiquated in certain aspects, for example, it's written in K&R C rather than C99; it has to manually compute certain things that are now defined in C standard library headers; there are no tests; and so on and so forth. All that the original code says by way of licensing is Released in the public domain by so and so; no BSD/MIT/GPL, just public domain.In addition to my original application, I'd like to release my own fork of the legacy library with a few of changes, chiefly to modernize it and to add unit tests. I've contacted the original author about it, but have not heard back from him. Am I within my rights to release my fork with a liberal (BSD/MIT) license? I'm not trying to make any money off of either my update of the legacy library or off of the application built on top of it.
License for forked software library
licensing
IANAL but I did find an interesting piece by an IP lawyer in the US, essentially declaring that the 'public domain is not a license':Just as there is nothing in the law that permits a person to dump  personal property on a public highway, there is nothing that permits  the dumping of copyrighted works into the public domain, except as  happens in due course when any applicable copyrights expire. Until  those copyrights expire, no mechanism is in the law by which an owner  of software can simply elect to place it in the public domain.It would appear that these caveats relate more to fear that the public-domain-ness of the work could be retracted any time by the original author.