I'm listening to this video lecture by ML Baker on "Tensors/tensor products over-mystified" and it's the most helpful discussion I've ever found https://www.youtube.com/watch?v=qHuUazkUcnU He keeps relating it to the isomorphism between a finite dimensional vector space and its double dual. David, perhaps you know all of this already, but I just want to note it. I very much appreciate his video lectures on category theory and also on elliptic functions and modular forms. I'm amazed at how much math he has already learned. He only has a master's degree.