Today I derive the famous Dirac equation. I talk about four-vector notation and contraction, as well as laying out the requirements for the anticommutator relation of gamma matrices.
Dot products of four vectors:
https://www.youtube.com/watch?v=eyxC4YJ0YH0
Deriving the Klein Gordon Equation:
https://www.youtube.com/watch?v=bPlP9EkGixk&t=3s