arXiv subjects
Publications and source records attributed to Shengqi Hu.
Inspired by Index I and II lemmas and Rauch I and II theorems, we formulate out an Index III lemma and Rauch III theorem in this paper. As applications, we present a Rauch's type theorem with lower Ricci curvature bound and a volume comparison result.
In this paper we show that, in the definition of Alexandrov spaces with lower or upper curvature bound, the original conditions can be replaced with much weaker ones. For the purpose, we introduce `imaginary' comparison angles (and `imaginary' angles), and the right or left bounded second derivative in the support sense. As applications, we provide new proofs for the Doubling Theorem, and the Globalization Theorem for complete or geodesic Alexandrov spaces with lower curvature bound.
This paper aims to give an elementary proof for Toponogov's theorem in Alexandrov geometry with lower curvature bound. The idea of the proof comes from the fact that, in Riemannian geometry, sectional curvature can be embodied in the second variation formula.