I am looking to expand my knowledge on set theory (which is pretty poor right now — basic understanding of sets, power sets, and different (infinite) cardinalities). Are there any books that come to your mind that would be useful for an undergrad math student who hasn’t taken a set theory course yet?
Thanks a lot for your suggestions!
I recommend Naive Set Theory by Halmos. It’s a friendly, thin and fun to read introduction to set theory.