Thanks to the kind offices of the folks at PARC!
I recommend the video, because you can see the slides, and there are some diagrams and stuff on those that I reference.
Errata: it’s actually 51% of the bracket 36-50. (That will make sense if you listen to the whole thing). And it’s Higinbotham with one G.
At some point, I’ll transcribe this and make it a page on the site…