Your answers are found in the saga of the readline wars (where every imaginable method to run around the GPL and make it meaningless has been tried). Broadly s

Your answers are found in the saga of the readline wars (where every imaginable method to run around the GPL and make it meaningless has been tried). Broadly speaking the rule of thumb is that if something makes use of internal knowledge of GPL code implementation or function (i.e. unique data structures/objects/functions that are not considered "standard"), it's considered a derivative work (this is also how the Linux kernel approaches GPL vs non-GPL drivers, too). If all it were to take was to adapt and repackage a GPL project as a dynamically loaded library, the GPL would be meaningless. In my mind, the really hairy area is where certain projects seem to be allowed to define "public" APIs that surrender GPL protection and allow use of closed binary libraries (i.e. the Linux kernel's public driver interface or Octave's MEX interface). Or what happens when the BSD folks just copy your API and re-implement everything (undermining the uniqueness of the GPL software's internals)? Don't bring this up to the FSF though, they suddenly switch from being eloquent to pretending to be dense.