Comparing a sorted-set with numbers to a set with keywords is not symmetric:
The latter case should return false instead of throwing.
Cause: APersistentMap.equiv() and APersistentSet.equiv() do not expect this exception be thrown from the containsKey()/contains() check.
Proposed: It would probably be best for PersistentTreeMap and PersistentTreeMap to implement equiv() and handle that possibility appropriately. Should also consider similar changes in equals() if necessary.
CLJ-1983 (downstream example with clojure.data/diff)