45. The Fundamental Theorem of Riemannian Geometry
We begin this lecture by proving the (somewhat grandiosely named) Fundamental Theorem of Riemannian Geometry, which states that if $(M,m)$ is a Riemannian manifold then there exists a unique connection $ \nabla$ on $M$ which is simultaneously Riemannian with respect to $m$ and torsion-free. This connection is usually called the Levi-Civita connection of $m$.
We then discuss the celebrated Berger Classification Theorem which enumerates the seven possible options for the holonomy group of a Riemannian metric.
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