@SuppressWarnings("unchecked")
  public static <K, V> ImmutableSetMultimap<K, V> of() {
    return (ImmutableSetMultimap<K, V>) EmptyImmutableSetMultimap.INSTANCE;
  }

  /** Returns an immutable multimap containing a single entry. */
  public static <K, V> ImmutableSetMultimap<K, V> of(K k1, V v1) {
    ImmutableSetMultimap.Builder<K, V> builder = ImmutableSetMultimap.builder();
    builder.put(k1, v1);
    return builder.build();

  @SuppressWarnings("unchecked")
  public static <K, V> ImmutableSetMultimap<K, V> of() {
    return (ImmutableSetMultimap<K, V>) EmptyImmutableSetMultimap.INSTANCE;
  }

  /** Returns an immutable multimap containing a single entry. */
  public static <K, V> ImmutableSetMultimap<K, V> of(K k1, V v1) {
    ImmutableSetMultimap.Builder<K, V> builder = ImmutableSetMultimap.builder();
    builder.put(k1, v1);
    return builder.build();

    assertEquals(ImmutableSetMultimap.of(1, "one"), ImmutableSetMultimap.of("one", 1).inverse());
    assertEquals(
        ImmutableSetMultimap.of(1, "one", 2, "two"),
        ImmutableSetMultimap.of("one", 1, "two", 2).inverse());
    assertEquals(
        ImmutableSetMultimap.of('o', "of", 'f', "of", 't', "to", 'o', "to"),
        ImmutableSetMultimap.of("of", 'o', "of", 'f', "to", 't', "to", 'o').inverse());
  }

    assertEquals(ImmutableSetMultimap.of(1, "one"), ImmutableSetMultimap.of("one", 1).inverse());
    assertEquals(
        ImmutableSetMultimap.of(1, "one", 2, "two"),
        ImmutableSetMultimap.of("one", 1, "two", 2).inverse());
    assertEquals(
        ImmutableSetMultimap.of('o', "of", 'f', "of", 't', "to", 'o', "to"),
        ImmutableSetMultimap.of("of", 'o', "of", 'f', "to", 't', "to", 'o').inverse());
  }

  // cached so that this.multimapView().inverse() only computes inverse once
  private transient @Nullable ImmutableSetMultimap<K, V> multimapView;

  public ImmutableSetMultimap<K, V> asMultimap() {
    ImmutableSetMultimap<K, V> result = multimapView;
    return (result == null)
        ? (multimapView =
            new ImmutableSetMultimap<K, V>(new MapViewOfValuesAsSingletonSets(), size(), null))
        : result;
  }

  // TODO: test ImmutableMultimap builder and factory methods

  public void testCopyOf() {
    ImmutableSetMultimap<String, String> setMultimap = ImmutableSetMultimap.of("k1", "v1");
    ImmutableMultimap<String, String> setMultimapCopy = ImmutableMultimap.copyOf(setMultimap);
    assertSame(
        "copyOf(ImmutableSetMultimap) should not create a new instance",
        setMultimap,
        setMultimapCopy);

    ImmutableSetMultimap<String, Integer> expected =
        ImmutableSetMultimap.of("one", 1, "won", 1, "two", 2, "too", 2, "three", 3);
    assertEquals(expected, map.asMultimap());
  }

  public void testAsMultimapWhenEmpty() {
    ImmutableMap<String, Integer> map = ImmutableMap.of();
    ImmutableSetMultimap<String, Integer> expected = ImmutableSetMultimap.of();

import java.util.Collection;

/**
 * Implementation of {@link ImmutableListMultimap} with no entries.
 *
 * @author Mike Ward
 */
@GwtCompatible
final class EmptyImmutableSetMultimap extends ImmutableSetMultimap<Object, Object> {
  static final EmptyImmutableSetMultimap INSTANCE = new EmptyImmutableSetMultimap();

  private EmptyImmutableSetMultimap() {
    super(ImmutableMap.<Object, ImmutableSet<Object>>of(), 0, null);
  }

  @LazyInit private transient @Nullable ImmutableSetMultimap<K, V> multimapView;

  /**
   * Returns a multimap view of the map.
   *
   * @since 14.0
   */
  public ImmutableSetMultimap<K, V> asMultimap() {
    if (isEmpty()) {
      return ImmutableSetMultimap.of();
    }
    ImmutableSetMultimap<K, V> result = multimapView;
    return (result == null)

  @LazyInit private transient @Nullable ImmutableSetMultimap<K, V> multimapView;

  /**
   * Returns a multimap view of the map.
   *
   * @since 14.0
   */
  public ImmutableSetMultimap<K, V> asMultimap() {
    if (isEmpty()) {
      return ImmutableSetMultimap.of();
    }
    ImmutableSetMultimap<K, V> result = multimapView;
    return (result == null)