This is incredibly cool, and I'd love to read similar work on other data structures. Unfortunately I rarely have a need for immutable sorted sequences.
Surprisingly expensive: In practice it can generate several levels over the course of a day depending on how much CPU power it is given and how large the desired levels are.
Need to reread to see if I really understand what they're doing. But this might be the approach I'll try for the project I'm reading this stuff for.
Catchy soundtrack, too.
I want to refer to this one roughly once a year, and it always takes me half an hour to find it. (Though usually I stumble onto other interesting papers during that search, so it's not too bad).
Amazing ITS restoration project. A lot of of other cool stuff under /PDP-10/ in general.