He kindly told me that he thought about it, and this is not a case of violation.
However, he did not tell me anything about header files, so I suppose
we must assume he still thinks the same on this since 2003.
From what I gather in his 2003 e-mail, I believe their lawyer must have
thought of the "fair use" exceptions in copyright law, and indeed
simply quoting a few typedefs would fall under fair use (since it is not a
substantial portion). On the other hand, I have a hard time believing
that this goes for anything in "header files", in general. I think you
would have to ask him about the opinion of the FSF on header files,
and interface definitions in general in any language. Note that he did
not mention "function declarations". Read what he says carefully:
> Someone recently made the claim that including a header file always
> makes a derivative work.
> That's not the FSF's view. Our view is that just using structure
> definitions, typedefs, enumeration constants, macros with simple
> bodies, etc., is NOT enough to make a derivative work. It would take
> a substantial amount of code (coming from inline functions or macros
> with substantial bodies) to do that.
He explicitly says that for there to be a derivative work, it would take
a substantial amount of code. So, you can't just take a substantial
portion of a GPL'd program's (either an application of a library) *interface*
and release it under an arbitrary license. That is simply not permitted by the license.
I think there are trolls from some companies here that are trying to make it seem as
if you can use GPL'd libraries in any proprietary program. I am beginning to
suspect they already do that in other ways.