"Well, a Riemann surface is a certain kind of Hausdorff space. You know what a
Hausdorff space is, don’t you? Its also compact, ok. I guess it is also a manifold.
Surely you know what a manifold is. Now let me tell you one non-trivial theorem,
the Riemann–Roch Theorem"
— Gian-Carlo Rota’s recollection of Lefschetz lecturing in the 1940’s