@ParametricNullness K fromKey, @ParametricNullness K toKey) {
    return subMap(fromKey, true, toKey, false);
  }

  @Override
  public NavigableMap<K, V> subMap(
      @ParametricNullness K fromKey,
      boolean fromInclusive,
      @ParametricNullness K toKey,
      boolean toInclusive) {
    return delegate().subMap(fromKey, fromInclusive, toKey, toInclusive);
  }

  @Override

      @ParametricNullness K fromKey, @ParametricNullness K toKey) {
    return subMap(fromKey, true, toKey, false);
  }

  @Override
  public NavigableMap<K, V> subMap(
      @ParametricNullness K fromKey,
      boolean fromInclusive,
      @ParametricNullness K toKey,
      boolean toInclusive) {
    return delegate().subMap(fromKey, fromInclusive, toKey, toInclusive);
  }

  @Override

    }

    @Override
    public NavigableMap<K, Collection<V>> headMap(@ParametricNullness K toKey) {
      return headMap(toKey, false);
    }

    @Override
    public NavigableMap<K, Collection<V>> headMap(@ParametricNullness K toKey, boolean inclusive) {
      return new NavigableAsMap(sortedMap().headMap(toKey, inclusive));
    }

    @Override

  @Override
  public ImmutableSortedMap<K, V> headMap(K toKey) {
    checkNotNull(toKey);
    return newView(sortedDelegate.headMap(toKey));
  }

  ImmutableSortedMap<K, V> headMap(K toKey, boolean inclusive) {
    checkNotNull(toKey);
    if (inclusive) {
      K tmp = higher(toKey);
      if (tmp == null) {
        return this;
      }
      toKey = tmp;
    }
    return headMap(toKey);
  }