Comparison Geometry asks: What can we say about a Riemannian manifold if we know a (lower or upper) bound for its curvature, and perhaps something about its topology? Powerful results that allow the exploration of this question were first obtained in the 1950s by Rauch, Alexandrov, Toponogov, and Bishop, with some ideas going back to Hopf, Morse, Schoenberg, Myers, and Synge in the 1930s. |