return immutableEntry(key, function.apply(key));
      }
    };
  }

  private static final class SortedAsMapView<K extends @Nullable Object, V extends @Nullable Object>
      extends AsMapView<K, V> implements SortedMap<K, V> {

    SortedAsMapView(SortedSet<K> set, Function<? super K, V> function) {
      super(set, function);
    }

    @Override
    SortedSet<K> backingSet() {

        return immutableEntry(key, function.apply(key));
      }
    };
  }

  private static final class SortedAsMapView<K extends @Nullable Object, V extends @Nullable Object>
      extends AsMapView<K, V> implements SortedMap<K, V> {

    SortedAsMapView(SortedSet<K> set, Function<? super K, V> function) {
      super(set, function);
    }

    @Override
    SortedSet<K> backingSet() {