Barrapunto

If the program dynamically links plug-ins [convendrás, supongo, que da igual que sea plugin o biblioteca], and they make function calls to each other and share data structures, we believe they form a single program, which must be treated as an extension of both the main program and the plug-ins. This means that combination of the GPL-covered plug-in with the non-free main program would violate the GPL.

[con el enlazado de bibliotecas] You therefore end up with two separate bodies of code that talk to each other only as needed, which would seem to eliminate any question of there being a derivative created. This is similar to simply referencing Scout Finch - perhaps I mention that my character has all the curiosity of Scout Finch, which calls to your mind her constant probing of the identify of Boo Radley. I don't actually copy any of the text from To Kill a Mockingbird, but simply reference it at 'run-time.' Just as this would be acceptable in literature (and wouldn't create a derivative work), so, too, it seems reasonable to believe that software that dynamically links to GPL code (including Linux) should be safe from the GPL's so-called "contamination."

Y también tienes el caso del Game Genie VS. Nintendo [resource.org] en EE.UU., donde los jueces dictaminaron que, para que fuese obra derivada, debía contener alguna parte del código sujeto al copyright. Algo que no ocurre cuando te limitas a usar la biblioteca.