His book _TeX and METAFONT_ (about the initial public release) goes into these difficulties in greater detail and includes the charming response by his wife when shown some initial efforts:

>Why don't you make them _S_ shaped?

To some degree, this problem was eventually solved, c.f., the five volume set _Computers and Typesetting_:

https://www-cs-faculty.stanford.edu/~knuth/abcde.html

but then one had the effort to create a new typeface set for math equations by the AMS, eventually named Euler as written up in "AMS Euler — a new typeface for mathematics". _Scholarly Publishing_ and so forth, but arguably, things went awry in that rather than capture the ductus of Prof. Zapf's pen, and model based on that stroke and a pen shape, the expedient approach of simply modeling the outline was arrived at and implemented due to the difficulty and lengthy time required for the idealized approach.

Another consideration may have been that there doesn't seem to be an available algorithm which is robust and accurate and automatic for determining the curves which describe the union of arbitrary Bézier curves (some projects get around this by making high resolution pixel images and tracing them).

For the work on Euler, this article¹ (https://www.sciencedirect.com/science/article/pii/S240587262...) goes into the whole Digital Typography program at Stanford for whom, one of the projects was creating those outlines for the Euler math fonts. It’s worth remembering that at the time, not only was Metafont the only outline-based font technology,² but things like scanners were rare to nonexistent and the bitmaps that were used to determine coordinates for the curves of the fonts were hand-drawn on fine-lined graph paper (and sent to Hermann Zapf for approval).

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1. Funnily enough this is the second time in two days that I’ve shared this article, albeit in different contexts.

2. As far as I know, although I could be wrong.