For context, you probably want to look at this HN comment[1], and the chain leading up to it from [2], as well as the followup [3]
[1] https://news.ycombinator.com/item?id=38877833 [2] https://news.ycombinator.com/item?id=38862446 [3] https://news.ycombinator.com/item?id=38878014
Basically, it's an exploration in trying and repeatedly failing understand k, and eventually figuring out roughly how to translate this: