I met him a few times when I was a grad student at Stony Brook (Physics). I can't speak for his particular math skills, but he's in possession of an incredibly

I met him a few times when I was a grad student at Stony Brook (Physics). I can't speak for his particular math skills, but he's in possession of an incredibly sharp mind. The Simons Center for Geometry and Physics has an art gallery and an associated lecture series, and James often shows up to participate in these events. Luckily, these events are free to enter for all graduate students. At one of these events, I'd commented that a particular piece reminded me of a crystalline structure I was interested in studying (as a li-ion cathode). James overheard me and came over to quiz me on some of my group's work. About 8 months later, I ran into him at another lecture. While he didn't remember my name, he asked how my hollandite simulations had turned out. This anecdote doesn't really prove anything, other than that Dr Simons is a pretty cool dude.