private final NavigableSet<E> forward;

    DescendingSet(NavigableSet<E> forward) {
      this.forward = forward;
    }

    @Override
    protected NavigableSet<E> delegate() {
      return forward;
    }

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

    @Override

	return nil
}

// Step takes a string provided from a server (or just an empty string for the
// very first conversation step) and attempts to move the authentication
// conversation forward.  It returns a string to be sent to the server or an
// error if the server message is invalid.  Calling Step after a conversation
// completes is also an error.

    WRAPPER_TO_PRIMITIVE_TYPE = Collections.unmodifiableMap(wrapToPrim);
  }

  private static void add(
      Map<Class<?>, Class<?>> forward,
      Map<Class<?>, Class<?>> backward,
      Class<?> key,
      Class<?> value) {
    forward.put(key, value);
    backward.put(value, key);
  }

  /**
   * Returns an immutable set of all nine primitive types (including {@code void}). Note that a

     *   <li>Other sources may not support resolution and return null</li>
     * </ul>
     * <p>
     * The implementation must handle:
     * <ul>
     *   <li>Both forward and back slashes as path separators</li>
     *   <li>Parent directory references (..)</li>
     *   <li>Both file and directory targets</li>
     * </ul>
     *

  @Override
  public NavigableMap<K, V> descendingMap() {
    return new DescendingMap();
  }

  private final class DescendingMap extends Maps.DescendingMap<K, V> {
    @Override
    NavigableMap<K, V> forward() {
      return AbstractNavigableMap.this;
    }

    @Override
    Iterator<Entry<K, V>> entryIterator() {
      return descendingEntryIterator();
    }
  }

 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>. The {@link
 * #delegate()} method must be overridden to return the instance being decorated.
 *
 * <p>This class does <i>not</i> forward the {@code hashCode} and {@code equals} methods through to
 * the backing object, but relies on {@code Object}'s implementation. This is necessary to preserve

 *   <li>{@link UnmodifiableIterator}
 *   <li>{@link UnmodifiableListIterator}
 * </ul>
 *
 * <h2>Forwarding collections</h2>
 *
 * We provide implementations of collections that forward all method calls to a delegate collection
 * by default. Subclasses can override one or more methods to implement the decorator pattern. For
 * an example, see {@link ForwardingCollection}.
 *
 * <h2>Other</h2>
 *

 * desired per the <a href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
 *
 * <p><b>{@code default} method warning:</b> This class does <i>not</i> forward calls to {@code
 * default} methods. Instead, it inherits their default implementations. When those implementations
 * invoke methods, they invoke methods on the {@code ForwardingExecutorService}.
 *

    private final NavigableSet<E> forward;

    DescendingSet(NavigableSet<E> forward) {
      this.forward = forward;
    }

    @Override
    protected NavigableSet<E> delegate() {
      return forward;
    }

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

    @Override

 * </ul>
 * <p>
 * Each build is only concerned with versions before it, as those are the ones that need to be tested
 * for backwards compatibility. We never look forward, and don't add forward facing version number to branches of previous
 * version.
 * <p>
 * Each branch has a current version, and expected compatible versions are parsed from the server code's Version` class.