Not the first time that a Nature publication's "too good to be true" results turn out to be based on simple programming errors... Nature 532, 210 (2016) was retracted after it was shown that a hand-coded gradient function, used in gradient descent, had a simple sign error (details in arXiv 2003.05808).
> Of course, if you're implementing POSIX vi, there are quite a few features that have aged poorly, like roff/troff macros and line-editing
What do you mean by "roff/troff macros"?
EDIT: Ah, you're probably talking about the "section-wise" movements, defined in POSIX with language like "A line whose first character is a <period> and whose second and third characters match a two-character pair in the 'sections' edit option (see ex)" - that's the first time I've stumbled upon the 'sections' and 'paragraphs' options in the Vim manual ... Very quaint!
Given a commit that both refactors (A) and adds a feature (B), you can go into the codebase and remove the new feature by hand (B^-1), commit the feature removal, and immediately revert the feature removal. This leads to three commits: (A B), B^-1, and B. Squash the first two commits to obtain a commit that only refactors, and another commit that only adds the new feature. I've written more about this technique ("the Hammer") here: https://github.com/Mortal/gittalk
In TypeScript it's called "bivariance", which sounds very programming language theory like, but is not a term typically used in academic contexts, since it is unsound almost by default. It's described here: https://www.typescriptlang.org/docs/handbook/type-compatibil...