If you’re studying General Relativity or Tensor Calculus you’ve slammed into the Riemann tensor and its flurry-of-gammas-and-indices definition. But at its heart, the Riemann is just saying “move a vector around a tiny parallelogram first one way and then the other. Get a different result one way? Then the space is curved.” This video matches up the symbols and indices to that basic definition. I always remember something better when it makes sense. This video should help you remember the Riemann’s definition too.