Does using a GPL v2.1 as a resource in studying count as derivative work?

Question

I came across source code for an AI that plays some classic video games. It's licensed as:

GNU LESSER GENERAL PUBLIC LICENSE Version 2.1, 

I understand the Gnu license pretty well and if I were to port or include the AI in a game I'm working on I'd need to include the source in my release, and make it free.

But what if I use it as a reference for design paradigms? Basically, I'd have my source code on my right screen, building it as I go, and on the left screen I'd have the AI published under GPL 2.1 for a reference. Technically, not a single line of the author's code would make it into my code.

But, in all fairness, the original author has solved a lot of the hard problems already and I'm using the solutions that they came up with through hours of experimentation and development. This seems to be a bit of a gray area and I haven't found an answer online to this question.

Answer 1

Copyright law protect the expression of an idea, but not the idea itself. This means that if you read the source code of the AI to distill some ideas from it, then you can apply those ideas to your own work without being affected by the copyright license of the AI.

However, when doing this you have to be careful, especially if you use those ideas in a similar context.
If your code starts to look similar to the code of the AI, then you might be affected by the original expression of the idea and that can make your code a derived work of the AI code and subject to the LGPL license.