What are top pure mathematicians experts in? How about top doctors? The easy answers would be "pure math" and "medicine", but these are a bit too vague to be satisfying (What is pure math? What is medicine?). They also don't capture all of what these experts excel at. To know what an expert of a particular type is truly expert at, we need to understand the system that creates that type of expert. What are these experts rewarded for doing or knowing? What actions make them more or less likely ...