public ContiguousSet<C> tailSet(C fromElement, boolean inclusive) {
    return tailSetImpl(checkNotNull(fromElement), inclusive);
  }

  /*
   * These methods perform most headSet, subSet, and tailSet logic, besides parameter validation.
   */
  @SuppressWarnings("MissingOverride") // Supermethod does not exist under GWT.
  abstract ContiguousSet<C> headSetImpl(C toElement, boolean inclusive);

  public ContiguousSet<C> tailSet(C fromElement, boolean inclusive) {
    return tailSetImpl(checkNotNull(fromElement), inclusive);
  }

  /*
   * These methods perform most headSet, subSet, and tailSet logic, besides parameter validation.
   */
  @SuppressWarnings("MissingOverride") // Supermethod does not exist under GWT.
  abstract ContiguousSet<C> headSetImpl(C toElement, boolean inclusive);

      return subMap(
          Range.range(
              fromKey, BoundType.forBoolean(fromInclusive),
              toKey, BoundType.forBoolean(toInclusive)));
    }

    @Override
    public NavigableMap<Cut<C>, Range<C>> headMap(Cut<C> toKey, boolean inclusive) {
      return subMap(Range.upTo(toKey, BoundType.forBoolean(inclusive)));
    }

    @Override

  /**
   * File Separator: These four information separators may be used within data in optional fashion,
   * except that their hierarchical relationship shall be: FS is the most inclusive, then GS, then
   * RS, and US is least inclusive. (The content and length of a File, Group, Record, or Unit are
   * not specified.)
   *
   * @since 8.0
   */
  public static final byte FS = 28;

  /**

  /**
   * File Separator: These four information separators may be used within data in optional fashion,
   * except that their hierarchical relationship shall be: FS is the most inclusive, then GS, then
   * RS, and US is least inclusive. (The content and length of a File, Group, Record, or Unit are
   * not specified.)
   *
   * @since 8.0
   */
  public static final byte FS = 28;

  /**

      @ParametricNullness K toKey,
      boolean toInclusive) {
    return delegate().subMap(fromKey, fromInclusive, toKey, toInclusive);
  }

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

  @Override
  public NavigableMap<K, V> tailMap(@ParametricNullness K fromKey, boolean inclusive) {

      @ParametricNullness K toKey,
      boolean toInclusive) {
    return delegate().subMap(fromKey, fromInclusive, toKey, toInclusive);
  }

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

  @Override
  public NavigableMap<K, V> tailMap(@ParametricNullness K fromKey, boolean inclusive) {

      for (boolean inclusive : new boolean[] {false, true}) {
        assertThat(navigableMap.headMap(key, inclusive).entrySet())
            .containsExactlyElementsIn(expected.headMap(key, inclusive).entrySet())
            .inOrder();
        assertThat(navigableMap.tailMap(key, inclusive).entrySet())
            .containsExactlyElementsIn(expected.tailMap(key, inclusive).entrySet())
            .inOrder();

      assertTrue(Thread.holdsLock(mutex));
      return delegate().floorKey(key);
    }

    @Override
    public NavigableMap<K, V> headMap(K toKey, boolean inclusive) {
      assertTrue(Thread.holdsLock(mutex));
      return delegate().headMap(toKey, inclusive);
    }

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

    @Override

        @ParametricNullness V toElement,
        boolean toInclusive) {
      return wrap(
          getSortedSetDelegate().subSet(fromElement, fromInclusive, toElement, toInclusive));
    }

    @Override
    public NavigableSet<V> headSet(@ParametricNullness V toElement, boolean inclusive) {
      return wrap(getSortedSetDelegate().headSet(toElement, inclusive));
    }

    @Override