public static <K, V> ImmutableSortedMap<K, V> copyOfSorted(SortedMap<K, ? extends V> map) {
    Comparator<? super K> comparator = map.comparator();
    if (comparator == null) {
      // If map has a null comparator, the keys should have a natural ordering,
      // even though K doesn't explicitly implement Comparable.
      comparator = (Comparator<? super K>) NATURAL_ORDER;
    }
    if (map instanceof ImmutableSortedMap) {

  public static <K, V> ImmutableSortedMap<K, V> copyOfSorted(SortedMap<K, ? extends V> map) {
    Comparator<? super K> comparator = map.comparator();
    if (comparator == null) {
      // If map has a null comparator, the keys should have a natural ordering,
      // even though K doesn't explicitly implement Comparable.
      comparator = (Comparator<? super K>) NATURAL_ORDER;
    }
    if (map instanceof ImmutableSortedMap) {

     * @param comparator the comparator for ordering the elements in the priority queue
     * @return a new instance of {@link PriorityBlockingQueue}
     * @see PriorityBlockingQueue#PriorityBlockingQueue(int, Comparator)
     */
    public static <E> PriorityBlockingQueue<E> newPriorityBlockingQueue(final int initialCapacity, final Comparator<? super E> comparator) {

      return standardTailSet(fromElement);
    }

    @SuppressWarnings("unchecked")
    @Override
    public Comparator<? super E> comparator() {
      Comparator<? super E> forwardComparator = forward.comparator();
      if (forwardComparator == null) {
        return (Comparator) Ordering.natural().reverse();
      } else {
        return reverse(forwardComparator);
      }
    }

      return standardTailSet(fromElement);
    }

    @SuppressWarnings("unchecked")
    @Override
    public Comparator<? super E> comparator() {
      Comparator<? super E> forwardComparator = forward.comparator();
      if (forwardComparator == null) {
        return (Comparator) Ordering.natural().reverse();
      } else {
        return reverse(forwardComparator);
      }
    }

    Comparator<TestDatum> comparator = Comparator.comparing(d -> d.letter);

    // When elements compare as equal (both C's have same letter), our merge should always return C1
    // before C2, since C1 is from the first iterator.

    Iterator<TestDatum> merged =
        Iterators.mergeSorted(ImmutableList.of(left.iterator(), right.iterator()), comparator);

    }

    @Override
    SortedSet<E> delegate() {
      return (SortedSet<E>) super.delegate();
    }

    @Override
    public @Nullable Comparator<? super E> comparator() {
      synchronized (mutex) {
        return delegate().comparator();
      }
    }

    @Override
    public SortedSet<E> subSet(E fromElement, E toElement) {
      synchronized (mutex) {

  public static <T extends @Nullable Object> UnmodifiableIterator<T> mergeSorted(
      Iterable<? extends Iterator<? extends T>> iterators, Comparator<? super T> comparator) {
    checkNotNull(iterators, "iterators");
    checkNotNull(comparator, "comparator");

    return new MergingIterator<>(iterators, comparator);
  }

  /**
   * An iterator that performs a lazy N-way merge, calculating the next value each time the iterator

  public static <T extends @Nullable Object> UnmodifiableIterator<T> mergeSorted(
      Iterable<? extends Iterator<? extends T>> iterators, Comparator<? super T> comparator) {
    checkNotNull(iterators, "iterators");
    checkNotNull(comparator, "comparator");

    return new MergingIterator<>(iterators, comparator);
  }

  /**
   * An iterator that performs a lazy N-way merge, calculating the next value each time the iterator

    }

    @Override
    SortedSet<E> delegate() {
      return (SortedSet<E>) super.delegate();
    }

    @Override
    public @Nullable Comparator<? super E> comparator() {
      synchronized (mutex) {
        return delegate().comparator();
      }
    }

    @Override
    public SortedSet<E> subSet(E fromElement, E toElement) {
      synchronized (mutex) {