assertEmpty(list);
      throw new Error();
    } catch (AssertionFailedError expected) {
    }
    try {
      assertEmpty(
          new Iterable<String>() {
            @Override
            public Iterator<String> iterator() {
              return singleton("a").iterator();
            }
          });
      throw new Error();
    } catch (AssertionFailedError expected) {
    }
  }

   * @since 11.0 (generics widened in 13.0)
   */
  public static <T> Iterable<T> presentInstances(
      Iterable<? extends Optional<? extends T>> optionals) {
    checkNotNull(optionals);
    return () ->
        new AbstractIterator<T>() {
          private final Iterator<? extends Optional<? extends T>> iterator =
              checkNotNull(optionals.iterator());

          @Override

    Iterator<String> iterator = list.iterator();
    assertTrue(iterator.hasNext());
    assertEquals("1", iterator.next());
    assertTrue(iterator.hasNext());
    assertEquals("2", iterator.next());
    assertTrue(iterator.hasNext());
    assertEquals("3", iterator.next());
    assertTrue(iterator.hasNext());
    assertEquals("4", iterator.next());
    assertFalse(iterator.hasNext());

   *
   * <p>Some algorithms that operate on a {@code PredecessorsFunction} may produce undesired results
   * if the returned {@link Iterable} contains duplicate elements. Implementations of such
   * algorithms should document their behavior in the presence of duplicates.
   *
   * <p>The elements of the returned {@code Iterable} must each be:
   *
   * <ul>
   *   <li>Non-null

   *
   * <p>Some algorithms that operate on a {@code SuccessorsFunction} may produce undesired results
   * if the returned {@link Iterable} contains duplicate elements. Implementations of such
   * algorithms should document their behavior in the presence of duplicates.
   *
   * <p>The elements of the returned {@code Iterable} must each be:
   *
   * <ul>
   *   <li>Non-null

        () -> {
          Iterator<String> iterator = values.iterator();
          iterator.next();
          iterator.remove();
        });

    Set<Entry<Integer, String>> entries = unmod.entrySet();
    assertThrows(
        UnsupportedOperationException.class,
        () -> {
          Iterator<Entry<Integer, String>> iterator = entries.iterator();
          iterator.next();

      return Collections.unmodifiableSet(adjacentNodeValues.keySet());
    } else {
      return new AbstractSet<N>() {
        @Override
        public UnmodifiableIterator<N> iterator() {
          Iterator<NodeConnection<N>> nodeConnections = orderedNodeConnections.iterator();
          Set<N> seenNodes = new HashSet<>();
          return new AbstractIterator<N>() {
            @Override
            protected @Nullable N computeNext() {

  /**
   * Returns a view of this range map as an unmodifiable {@code Map<Range<K>, V>}. Modifications to
   * this range map are guaranteed to read through to the returned {@code Map}.
   *
   * <p>The returned {@code Map} iterates over entries in ascending order of the bounds of the
   * {@code Range} entries.
   *
   * <p>It is guaranteed that no empty ranges will be in the returned {@code Map}.
   */
  Map<Range<K>, V> asMapOfRanges();

  }

  @Override
  public @Nullable K lastKey() {
    return sortedDelegate.lastKey();
  }

  @Nullable K higher(K k) {
    Iterator<K> iterator = keySet().tailSet(k).iterator();
    while (iterator.hasNext()) {
      K tmp = iterator.next();
      if (comparator().compare(k, tmp) < 0) {
        return tmp;
      }
    }
    return null;
  }

  @Override

      @Override
      public UnmodifiableIterator<E> iterator() {
        Iterable<E> incidentEdges =
            (selfLoopCount == 0)
                ? Iterables.concat(inEdgeMap.keySet(), outEdgeMap.keySet())
                : Sets.union(inEdgeMap.keySet(), outEdgeMap.keySet());
        return Iterators.unmodifiableIterator(incidentEdges.iterator());
      }

      @Override
      public int size() {