[Terr_]

I don't think I've put the same amount of thought into it, but my gut feeling is:

1. If you're summarizing "a contiguous chunk exists from A to B", that would require a mutable rebalancing tree and the borders constantly shift and merge and subdivide.

2. If you're instead just summarizing "the range between constant indices X-Y is [1/0/both] right now", then that can be done with a fixed tree arrangement that can have an exact layout in memory.

A simple example of the latter would be 8 leaves of 01110000, 4 parents of [both, 1, 0, 0], 2 grandparents of [both, 0], etc. The 3-value aspects could also be encoded into two bitmasks, if "has a 1" and "has a 0".