Riemann 1854 + Levi-Civita 1917: g_{mu nu} symmetric non-degenerate (0,2)-tensor; defines lengths + angles + Levi-Civita connection; basis of GR + sigma models.
Riemann 1854 + Levi-Civita 1917: g_{mu nu} symmetric non-degenerate (0,2)-tensor; defines lengths + angles + Levi-Civita connection; basis of GR + sigma models.