Every branch of mathematics I've seen so far works with sets and functions as core building blocks for its definitions.
What's a branch in math that use functions very little or maybe not at all?
Pardon if this question is too meta for this site, if so tell me where it fits better.
Note: This is not about me being uncomfortable about the definition. It's more that I learned about functions in middle school and back then didn't realize at all what scope of uses this definition comprises, but I still can't really pinpoint what was missing in my view. Habituation is not the same as understanding apparently.