Proof of the Toponogov Conjecture on Complete Surfaces

Brendan Guilfoyle, Wilhelm Klingenberg

Published 2020-02-28Version 1

We prove a conjecture of Toponogov on complete convex surfaces, namely that such surfaces must contain an umbilic point, albeit at infinity. Our proof is indirect. It uses Fredholm regularity of an associated Riemann-Hilbert boundary value problem and an existence result for holomorphic discs with Lagrangian boundary conditions, both of which apply to a putative counterexample. Corollaries of the main theorem include a Hawking-Penrose singularity-type theorem, as well as the proof of a conjecture of Milnor's from 1965 in the convex case.