We currently have a function mapMonotonic in Data.Set and one called mapKeysMonotonic in Data.Map. These names are confusing for two reasons: 1. In some mathematical contexts, a function is considered monotonic if it's *either* increasing or decreasing. 2. Even where monotonic specifically means *increasing*, it generally does *not* specifically mean *strictly increasing*. The functions in question work when, and only when, the given function is strictly increasing on the elements/keys in the set/map. I'd like to DEPRECATE these functions, and add new ones: Data.Set: mapStrictlyIncreasing and mapStrictlyDecreasing Data.Map: mapKeysStrictlyIncreasing and mapKeysStrictlyDecreasing Data.Map presents another possibility, however. We could make the replacements more general, giving them types Ord k => (k -> v -> (k', v')) -> Map k v -> Map k' v' and allowing the user to map over both keys and values in one pass. David Feuer