Category Theory III 2.1: String Diagrams part 1

String diagrams: Functors and natural transformations

[TmooreSweden]

Thanks for putting these up online they're thoroughly enjoyable to watch!
There are a constant humming going on in the background of the noice that should be easily avoidable using some easily abtainable audio program. Some audio devices increases that tiny irritating sound to a level that makes it a bit hard to concentrate on what you're teaching.

[isaacdefrain]

Half choose the left-to-right convention, the other half choose the left-to-right convention... Well, I guess it's settled then :)
But seriously though, did string diagrams come from Poincare duality?