I've never really been sure how licensing / relicensing work. I am trying to figure out first: what it means for a license to be GPL compatible (because I think I'm misunderstanding); second: is Apache 2 compatible with v3. According to a third party (.. can''t remember who sorry), FSF says no but Apache says yes. And third: if I fork something, then modify it, do I now have the authority to copyleft it as I wish or can compatibility bite me.