Hello! I'm not sure if this is the correct sub to post in. My boyfriend is a big math nerd, majoring in mathematics, and a freshman in college. I want to send him a gift of some sort, maybe a book that he'd enjoy/help him out. Or some sort of trinket. For his first semester he's taking Calculus III and intro to higher math, and his areas of interest include:
-differential geometry
-dynamical systems
-topology
-measure theory
If anyone could help me out it'd be much appreciated, or if this isn't the correct sub please direct me there 🙏 thank you!