The arities of the special union, intersection and difference operations don't match the arities of those in clojure.set.
| :-- | :-- | :-- | :-- |
|union | 0, 1, 2, n | 2 |
|intersection | 1, 2, n | 2 |
|difference | 1, 2, n | 2 |
This prevents using int-sets as a drop-in replacement for sets.
Looking at the source of clojure.set, those seem to be implemented via simple reduce for difference, and bubbled-sets (via bubble-max-key) for union and intersection.
Could a similar approach be used here? I'm willing to work on this.