public static <S> ElementOrder<S> unordered() {
    return new ElementOrder<>(Type.UNORDERED, null);
  }

  /**
   * Returns an instance which specifies that ordering is guaranteed to be always be the same across
   * iterations, and across releases. Some methods may have stronger guarantees.
   *
   * <p>This instance is only useful in combination with {@code incidentEdgeOrder}, e.g. {@code

  public static <S> ElementOrder<S> unordered() {
    return new ElementOrder<>(Type.UNORDERED, null);
  }

  /**
   * Returns an instance which specifies that ordering is guaranteed to be always be the same across
   * iterations, and across releases. Some methods may have stronger guarantees.
   *
   * <p>This instance is only useful in combination with {@code incidentEdgeOrder}, e.g. {@code

     */
    return Collector.of(
        () -> new ImmutableSortedMap.Builder<K, V>(comparator),
        (builder, input) -> builder.put(keyFunction.apply(input), valueFunction.apply(input)),
        ImmutableSortedMap.Builder::combine,
        ImmutableSortedMap.Builder::buildOrThrow,
        Collector.Characteristics.UNORDERED);
  }

 *
 * <ul>
 *   <li>directed graphs
 *   <li>undirected graphs
 *   <li>graphs that do/don't allow parallel edges
 *   <li>graphs that do/don't allow self-loops
 *   <li>graphs whose nodes/edges are insertion-ordered, sorted, or unordered
 *   <li>graphs whose edges are unique objects
 * </ul>
 *
 * <h3>Building a {@code Network}</h3>
 *
 * <p>The implementation classes that {@code common.graph} provides are not public, by design. To

      Collector.of(
          ToOptionalState::new,
          ToOptionalState::add,
          ToOptionalState::combine,
          ToOptionalState::getOptional,
          Collector.Characteristics.UNORDERED);

  /**
   * A collector that converts a stream of zero or one elements to an {@code Optional}.
   *
   * @throws IllegalArgumentException if the stream consists of two or more elements.

 * terms</a>):
 *
 * <ul>
 *   <li>directed graphs
 *   <li>undirected graphs
 *   <li>graphs that do/don't allow self-loops
 *   <li>graphs whose nodes/edges are insertion-ordered, sorted, or unordered
 *   <li>graphs whose edges have associated values
 * </ul>
 *
 * <p>{@code ValueGraph}, as a subtype of {@code Graph}, explicitly does not support parallel edges,

 *
 * <ul>
 *   <li>directed graphs
 *   <li>undirected graphs
 *   <li>graphs that do/don't allow parallel edges
 *   <li>graphs that do/don't allow self-loops
 *   <li>graphs whose nodes/edges are insertion-ordered, sorted, or unordered
 *   <li>graphs whose edges are unique objects
 * </ul>
 *
 * <h3>Building a {@code Network}</h3>
 *
 * <p>The implementation classes that {@code common.graph} provides are not public, by design. To

 * terms</a>):
 *
 * <ul>
 *   <li>directed graphs
 *   <li>undirected graphs
 *   <li>graphs that do/don't allow self-loops
 *   <li>graphs whose nodes/edges are insertion-ordered, sorted, or unordered
 * </ul>
 *
 * <p>{@code Graph} explicitly does not support parallel edges, and forbids implementations or
 * extensions with parallel edges. If you need parallel edges, use {@link Network}.
 *

 * terms</a>):
 *
 * <ul>
 *   <li>directed graphs
 *   <li>undirected graphs
 *   <li>graphs that do/don't allow self-loops
 *   <li>graphs whose nodes/edges are insertion-ordered, sorted, or unordered
 * </ul>
 *
 * <p>{@code Graph} explicitly does not support parallel edges, and forbids implementations or
 * extensions with parallel edges. If you need parallel edges, use {@link Network}.
 *

                OverConstrainedVersionException.class, () -> collect(createSet(new Object[] {a.artifact})));
        assertTrue(e.getMessage().contains("[3.2.1-v3235e, 3.3.0-v3346]"), "Versions unordered");
        assertTrue(e.getMessage().contains("Path to dependency:"), "DependencyTrail unresolved");
    }

    private Artifact getArtifact(String id, Set artifacts) {
        for (Object artifact : artifacts) {