As other commentors have pointed out [1], it appears to be a Tiered Vector implementation [2]. [1] https://news.ycombinator.com/item?id=20873110 https://news.y

As other commentors have pointed out [1], it appears to be a Tiered Vector implementation [2]. [1] https://news.ycombinator.com/item?id=20873110 https://news.ycombinator.com/item?id=20873110 [2] https://www.ics.uci.edu/~goodrich/pubs/wads99.pdf https://www.ics.uci.edu/~goodrich/pubs/wads99.pdf