    "A comparator for [[Entry]]s which compares their keys
     according to the given [[comparing]] function.

         value sortedEntries = map.sort(byKey(byIncreasing(String.lowercased)));

     This function is intended for use with [[Iterable.sort]]
     and [[Iterable.max]]."
    see (`function byItem`)
    shared Comparison byKey<Key>(Comparison comparing(Key x, Key y))
                (Key->Object x, Key->Object y)
            given Key satisfies Object =>
                    comparing(x.key, y.key);