android/guava/src/com/google/common/collect/Maps.java
private static <K, V> Map<K, V> filterFiltered(
      AbstractFilteredMap<K, V> map, Predicate<? super Entry<K, V>> entryPredicate) {
    return new FilteredEntryMap<>(
        map.unfiltered, Predicates.<Entry<K, V>>and(map.predicate, entryPredicate));
  }
private static <K, V> Map<K, V> filterFiltered(
      AbstractFilteredMap<K, V> map, Predicate<? super Entry<K, V>> entryPredicate) {
    return new FilteredEntryMap<>(
        map.unfiltered, Predicates.<Entry<K, V>>and(map.predicate, entryPredicate));
  }
Support {@code clear()}, {@code removeAll()}, and {@code retainAll()} when filtering a filtered
map.