The emphasized part is saying that the final palindrome should never have a letter appearing more in it than in the original string.

So you can't do aaabb -> aabbaa, because that would turn a's, count from 3 to 4. You could do aaabb -> abba though, as 2 <= 3.

I do agree that the description is quite lacking, but as this doesn't seem like a suggestion, I'm marking as resolved.

Review the definition of factor: https://www.britannica.com/science/factor-mathematics

You're thinking about prime factors, and that's another thing.

This version of kata does not have inputs with adjacent +.

This has been changed by Voile. Now the function expects long long and it's ok.

that's a cycle, it's out of the scope of the problem, afaik.

You can check whether that's the case

> maxBound :: Int
9223372036854775807