John Carlos Baez on Nostr: - "mixed variance tensor 𝑝ᵢᵏ" is how physicists say "matrix". You can take a ...

- "mixed variance tensor 𝑝ᵢᵏ" is how physicists say "matrix". You can take a trace of a matrix, which involves summing over indices: 𝑝ᵢⁱ in the Einstein summation convention. I was perhaps getting too fancy and multiplying matrices, which also involves summing over indices: 𝑝ᵢʲ𝑞ⱼᵏ or something like that. The point is that ALL THESE INDEX GYMNASTICS HAVE CATEGORIFIED ANALOGUES, DEFINED USING COENDS!!!