When are you violating a license like the GPL?

Specifically in the following scenarios where you're working on an open source library using an incompatible license like the MIT license.

• You copy & paste a method from a GPL library - blatantly a violation assuming the GPL library created the method themselves.


• You create a function with a similar purpose but you create it from scratch - presumably not a violation


• You use the same code as a GPL library, but you improve on it (optimize performance for example) - is this a violation?


• You use the same code as a GPL library, but you superficially refactor it (e.g. rename variables for clarity, add comments, but don't really change the underlying logic) - is this a violation?


• You translate code from a GPL library to another language but keep the logic exactly the same - presumably not a violation?

I know these are possibly questions for lawyers but I'm hoping to get a rough idea.