@Override
  public @Nullable E lower(E element) {
    return forward.higher(element);
  }

  @Override
  public @Nullable E floor(E element) {
    return forward.ceiling(element);
  }

  @Override
  public @Nullable E ceiling(E element) {
    return forward.floor(element);
  }

  @Override
  public @Nullable E higher(E element) {
    return forward.lower(element);
  }

  @Override

    ToOptionalState<T> combine(ToOptionalState<T> other) {
      if (element == null) {
        return other;
      } else if (other.element == null) {
        return this;
      } else {
        if (extras.isEmpty()) {
          // Replace immutable empty list with mutable list.
          extras = new ArrayList<>();
        }
        extras.add(other.element);
        extras.addAll(other.extras);

    Iterator<E> iterator = collection.iterator();
    Object element = iterator.next();
    // If it's an Entry, it may become invalid once it's removed from the Map. Copy it.
    if (element instanceof Entry) {
      Entry<?, ?> entry = (Entry<?, ?>) element;
      element = mapEntry(entry.getKey(), entry.getValue());
    }
    assertTrue(collection.contains(element)); // sanity check
    iterator.remove();

  @Override
  void setCountCheckReturnValue(E element, int count) {
    assertEquals(
        "multiset.setCount() should return the old count",
        getMultiset().count(element),
        setCount(element, count));
  }

  @Override
  void setCountNoCheckReturnValue(E element, int count) {
    setCount(element, count);
  }

  @CanIgnoreReturnValue
  private int setCount(E element, int count) {

    }

    /**
     * Removes the model version element from a POM editor.
     * This is used during inference when the model version can be inferred.
     *
     * @param document the XML document
     * @return true if the element was removed, false if it didn't exist
     */
    public static boolean removeModelVersion(Document document) {
        Element root = document.root();
        if (root == null) {

    }

    Builder() {}

    /**
     * Adds {@code element} to the {@code ImmutableCollection} being built.
     *
     * <p>Note that each builder class covariantly returns its own type from this method.
     *
     * @param element the element to add
     * @return this {@code Builder} instance
     * @throws NullPointerException if {@code element} is null
     */
    @CanIgnoreReturnValue

    assertEquals("Should be able to peek() at first element", "A", peekingIterator.peek());
    assertEquals(
        "Should be able to peek() first element multiple times", "A", peekingIterator.peek());
    assertEquals(
        "next() should still return first element after peeking", "A", peekingIterator.next());

    assertEquals("Should be able to peek() at middle element", "B", peekingIterator.peek());
    assertEquals(

  @Override
  public @Nullable E lower(E element) {
    return forward.higher(element);
  }

  @Override
  public @Nullable E floor(E element) {
    return forward.ceiling(element);
  }

  @Override
  public @Nullable E ceiling(E element) {
    return forward.floor(element);
  }

  @Override
  public @Nullable E higher(E element) {
    return forward.lower(element);
  }

  @Override

 */
final class SingletonImmutableSet<E> extends ImmutableSet<E> {
  private final E element;

  SingletonImmutableSet(E element) {
    this.element = checkNotNull(element);
  }

  @Override
  public int size() {
    return 1;
  }

  @Override
  public UnmodifiableIterator<E> iterator() {
    return Iterators.singletonIterator(element);
  }

  @Override
  public boolean contains(@Nullable Object object) {

        """.trimIndent()
        )
        val writer = NodeWriter(this, "    ")
        writer.node("graph TD")
        for (element in elements) {
            if (element is Platform) {
                writer.platform(element)
            } else {
                writer.element(element)
            }
        }
        println(endDiagram)
    }

    private fun NodeWriter.platform(platform: Platform) {