It's very strange to see handwriting lumped in with typewriting, to be described as limited relative to screens! Iverson notation was a 2D format (both in handwriting and typeset publications) making use of superscripts, subscripts, and vertical stacking like mathematics. It was linearized to allow for computer execution, but the designers described this as making the language more general rather than less:

> The practical objective of linearizing the typography also led to increased uniformity and generality. It led to the present bracketed form of indexing, which removes the rank limitation on arrays imposed by use of superscripts and subscripts.

(https://www.jsoftware.com/papers/APLDesign.htm)

I think this is more true than they realized at that time. The paper describes the outer product, which in Iverson notation was written as a function with a superscript ∘ and in APL became ∘. followed by the function. In both cases only primitive functions were allowed, that is, single glyphs. However, APL's notation easily extends to any function used in an outer product, no matter how long. But Iverson notation would have you write it in the lower half of the line, which would quickly start to look bad.