Complex analysis is one of my favorite areas of mathematics . It is truly beautiful and wonderfully marries complex numbers with calculus. So many of the theorems of real analysis gain new light in complex analysis
Type theory solidified my understanding of the relationship between computers and mathematics, and how mathematics can directly be applied to computer science. By having computers execute proofs using type theory I gained a new appreciation for rigor of proofs.
Abstract Algebra demonstrated to me that mathematics is all about abstraction. I now see groups everywhere, from vectors to the complex numbers, and I feel I can now look at the world of mathematics through the lens of groups, rings and fields.