To be clear, my understanding of the GC is that what I wrote would use a linear amount of storage before the gc and potentially an exponential amount after. But maybe the gc runs in more places than I’d realised and so it never gets to only be linear.
I've recorded a screencast of your algorithm running in Blinkenlights. That might help intuitively explain what the ABC Garbage Collector is doing: https://justine.lol/sectorlisp2/binarytree2.mp4
