backporting and dual-licensing
Say a person X writes a library libfoo. He licenses the library out
under both the GPL and a commercial licence.
A person Y uses libfoo under the GPL. He goes and does a lot of
improvements in the library since it is under the GPL. Now the modified
version of libfoo is copyrighted by both X and Y.
So X would not be able to import such improvements into the main
distribution of libfoo since then he would not be able to dual-licence
it - specifically he would not be able to licence it commercially, not
owning it entirely. He must either take Y into his business or obtain a
waiver from Y by one-time payment or whatever.
My question is: What would be considered a big enough
difference/modification that X would need Y's permission for backporting
1. If Y fixes a bug (of whatever severity) with a patch?
2. If Y makes improvements to the library by optimizing some algorithms?
3. If Y adds new functionality to the library?
4. If Y just restructures the library in a more efficient manner.