I feel like this is actually quite hard for an AI. To talk about formal systems like mathematics in an intuitive sense, we need language. And language requires us to have almost every other system (except perhaps vision). In particular, we would need sophisticated systems for dealing with categories.

I personally think that the simplest AI-hard problem is coming up with a satisfactory system for category formation and inference. See for instance Goldstone and Kerstein's chapter 22 in the Handbook of Psychology for a discussion of the problem.

I actually disagree with wikipedia's claim that vision is AI-hard. I think we could have good vision systems without a strong AI, and vice versa, although the latter would be quite crippled initially.