How does Feynman rank as a mathematician in comparison to pure mathematicians of the 20th century, we'll forget about Euler and Gauss. I'm more interested in logic than I am math and consequently I was not able to get beyond calculus, linear algebra and differential equations and some set theory, so I'm really not capable of evaluating Feynman's math work. I am quite skeptical of pure mathematics, especially set theory. I find it suspicious and unrigorous. Feynman on the other hand applied mathematics to physics and consequently I am much more willing to believe his mathematics than say Wiles' proof of Fermat's Last Theorem.