> There’s a pretty fuzzy line between something appropriate for the end of undergrad versus the beginning of grad school.
I agree. I've come across countless math textbooks claiming to be aimed at "beginning grad students and advanced undergrads." There's a lot of variability in that cross section of readers. Thinking back to my own senior year as an undergrad, some of my peers were extremely bright and were bound for top grad school programs, and some were just barely scraping by managing to graduate by the skin of their teeth.
I agree. I've come across countless math textbooks claiming to be aimed at "beginning grad students and advanced undergrads." There's a lot of variability in that cross section of readers. Thinking back to my own senior year as an undergrad, some of my peers were extremely bright and were bound for top grad school programs, and some were just barely scraping by managing to graduate by the skin of their teeth.