Ok, now onto the Levi-Civita connection. Fix a manifold {M} with the pseudo-metric {g}. This means essentially a metric, except that {g} as a bilinear form on the tangent spaces is still symmetric and nondegenerate but not necessarily positive definite. It is still possible to say that a pseudo-metric is compatible with a given connection.

This is the fundamental theorem of Riemannian geometry:

Theorem 1 There is a unique symmetric connection {\nabla} on {M} compatible with {g}. (more…)