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I think sorted-set (PersistentTreeSet) should implement the transient interface. It's a special-purpose set and should be usable just like every normal set.
Comment made by: hircus
Note that this would require PersistentTreeMap to implement IEditableCollection as well.
Comment made by: jafingerhut
Anyone wishing for sorted sets/maps with transients should consider the data.avl library, which has them: https://github.com/clojure/data.avl