Use of the API is usually interpreted as forming a derivative work under
copyright law, and I'm certain it's the FSF's interpretation, which is
what counts here.
Actually, no, the FSF is the only legal entity known to mankind that interprets copyright law in that fashion, and has so far avoided the question coming up in litigation. US copyright law is quite clear that you cannot create a derivative work simply by using the work. The API may be used if it is described anywhere under terms that allow reuse without restriction, including if it is described in a classroom or lecture environment. However, other aspects of the API (such as comments within the header files) cannot be copied without creating a derivative work.
If you want to be sure, though, ask the copyright holder and be prepared to delete the file if they say that it is derived.
BTW, this has nothing to do with the 2.0 compatibility issue, which has not yet been resolved.
....Roy
