* OutOfMemoryError}). This class does not permit {@code null} elements. A priority queue relying on
 * {@linkplain Comparable natural ordering} also does not permit insertion of non-comparable objects
 * (doing so results in {@code ClassCastException}).
 *
 * <p>This class and its iterator implement all of the optional methods of the {@link

 * 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}.
 *

      // already started execution. Because each task on a TaskNonReentrantExecutor can only produce
      // one execute() call to another instance from the same ExecutionSequencer, we know by
      // induction that the task that launched this one must not have added any other runnables to
      // that thread's queue, and thus we cannot be replacing a TaskAndThread object that would

 * 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,

   * types that contain an embedded IPv4 address.
   *
   * <p>NOTE: ISATAP addresses are explicitly excluded from this method due to their trivial
   * spoofability. With other transition addresses spoofing involves (at least) infection of one's
   * BGP routing table.
   *
   * @param ip {@link Inet6Address} to be examined for embedded IPv4 client address
   * @return {@code true} if there is an embedded IPv4 client address
   * @since 7.0
   */

 * terms</a>):
 *
 * <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 <a
 *       href="https://github.com/google/guava/wiki/GraphsExplained#uniqueness">unique</a> objects
 * </ul>
 *
 * <h3>Building a {@code Network}</h3>
 *

    assertFalse(manager.isHealthy());
    assertTrue(listener.stoppedCalled);
    assertTrue(listener.failedServices.isEmpty());
    // check that our NoOpService is not directly observable via any of the inspection methods or
    // via logging.
    assertEquals("ServiceManager{services=[]}", manager.toString());
    assertTrue(manager.servicesByState().isEmpty());
    assertTrue(manager.startupTimes().isEmpty());

      // already started execution. Because each task on a TaskNonReentrantExecutor can only produce
      // one execute() call to another instance from the same ExecutionSequencer, we know by
      // induction that the task that launched this one must not have added any other runnables to
      // that thread's queue, and thus we cannot be replacing a TaskAndThread object that would

 * average, in the marking phase, not {@code 5.0} as in {@code java.util.HashSet}.
 *
 * <p>If there are no removals, then {@link #iterator iteration} order is the same as insertion
 * order. Any removal invalidates any ordering guarantees.
 *
 * <p>This class should not be assumed to be universally superior to {@code java.util.HashSet}.