Indeed, pre-TeX, Phyllis Winkler prepared all of Knuth's papers using TYPIT sticks for all the math symbols. Unfortunately, I didn't nab her typewriter and TYPIT box after her retirement, but here's a good set of photos and explanation: https://twitter.com/mwichary/status/1098850604640755712?lang...

Also, a TYPIT advertisement on the bottom left of the third page of https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=6500767