A visual introduction to Riemannian curvatures and some discrete generalizations

We try to provide a visual introduction to some objects used in Riemannian geometry: parallel transport, sectional curvature, Ricci curvature, Bianchi identities... We then explain some of the strategies used to define ana- logues of curvature in non-smooth or discrete spaces, beginning with Alexan- drov curvature and δ-hyperbolic spaces, and insisting on various notions of generalized Ricci curvature, which we briefly compare.

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