Such a beautiful article! What tools did you use to draw the diagrams?

I've been working on a generalization of graphical tensor notation to include general functions. This is useful when combined with Penrose's "Covariant Derivative" notation and allows you to mechanistically symbolically compute the derivative of complicated tensor networks with respect to arbitrary tensors: https://github.com/thomasahle/tensorgrad

I'd be curious to know what you think about the design choices involved, given your excellent distillation & pedagogy powers.