}

  abstract ImmutableSet<Entry<K, V>> createEntrySet();

  @LazyInit @RetainedWith @CheckForNull private transient ImmutableSet<K> keySet;

  /**
   * Returns an immutable set of the keys in this map, in the same order that they appear in {@link
   * #entrySet}.
   */
  @Override
  public ImmutableSet<K> keySet() {
    ImmutableSet<K> result = keySet;

            .put("X_WEBKIT_CSP", "X-WebKit-CSP")
            .put("X_WEBKIT_CSP_REPORT_ONLY", "X-WebKit-CSP-Report-Only")
            .buildOrThrow();
    ImmutableSet<String> uppercaseAcronyms =
        ImmutableSet.of(
            "CH", "ID", "DNT", "DNS", "DPR", "ECT", "HTTP2", "IP", "MD5", "P3P", "RTT", "TE", "UA",
            "UID", "URL", "WWW", "XSS");

            .put("X_WEBKIT_CSP", "X-WebKit-CSP")
            .put("X_WEBKIT_CSP_REPORT_ONLY", "X-WebKit-CSP-Report-Only")
            .buildOrThrow();
    ImmutableSet<String> uppercaseAcronyms =
        ImmutableSet.of(
            "CH", "ID", "DNT", "DNS", "DPR", "ECT", "GPC", "HTTP2", "IP", "MD5", "P3P", "RTT", "TE",
            "UA", "UID", "URL", "WWW", "XSS");

    }

    ImmutableSet<R> rowSpace =
        (rowComparator == null)
            ? ImmutableSet.copyOf(rowSpaceBuilder)
            : ImmutableSet.copyOf(ImmutableList.sortedCopyOf(rowComparator, rowSpaceBuilder));
    ImmutableSet<C> columnSpace =
        (columnComparator == null)
            ? ImmutableSet.copyOf(columnSpaceBuilder)

      @Override
      public ImmutableSet<Object> create(List<?> list) {
        ImmutableSet.Builder<Object> builder = ImmutableSet.builder();
        for (Object o : list) {
          builder.add(o);
        }
        return builder.build();
      }
    },
    BUILDER_ADD_ARRAY {
      @Override
      public ImmutableSet<Object> create(List<?> list) {
        ImmutableSet.Builder<Object> builder = ImmutableSet.builder();

    }
  }

  // see https://github.com/google/guava/issues/2587
  private static final ImmutableSet<String> SCOPE_IDS =
      ImmutableSet.of("eno1", "en1", "eth0", "X", "1", "2", "14", "20");

  public void testIPv4AddressWithScopeId() {
    ImmutableSet<String> ipStrings = ImmutableSet.of("1.2.3.4", "192.168.0.1");
    for (String ipString : ipStrings) {
      for (String scopeId : SCOPE_IDS) {

    Set<Set<Integer>> expected = newHashSet();
    expected.add(ImmutableSet.<Integer>of());
    expected.add(ImmutableSet.of(1));
    expected.add(ImmutableSet.of(2));
    expected.add(ImmutableSet.of(3));
    expected.add(ImmutableSet.of(1, 2));
    expected.add(ImmutableSet.of(1, 3));
    expected.add(ImmutableSet.of(2, 3));
    expected.add(ImmutableSet.of(1, 2, 3));

  }

  @GwtIncompatible // ArrayTable
  public void testEqualsObjectNullValues() {
    new EqualsTester()
        .addEqualityGroup(INSTANCE)
        .addEqualityGroup(ArrayTable.create(ImmutableSet.of('A'), ImmutableSet.of(1)))
        .testEquals();
  }

  public void testToString() {
    assertEquals("{}", INSTANCE.toString());
  }

  public void testSize() {
    assertEquals(0, INSTANCE.size());
  }

  }

  @GwtIncompatible // ArrayTable
  public void testEqualsObjectNullValues() {
    new EqualsTester()
        .addEqualityGroup(INSTANCE)
        .addEqualityGroup(ArrayTable.create(ImmutableSet.of('A'), ImmutableSet.of(1)))
        .testEquals();
  }

  public void testToString() {
    assertEquals("{}", INSTANCE.toString());
  }

  public void testSize() {
    assertEquals(0, INSTANCE.size());
  }

  private static final ImmutableSet<String> PS_NOT_RS =
      ImmutableSet.of("blogspot.com", "blogspot.co.uk", "uk.com");

  private static final ImmutableSet<String> PS =
      ImmutableSet.<String>builder().addAll(RS).addAll(PS_NOT_RS).build();

  private static final ImmutableSet<String> NO_PS =
      ImmutableSet.of("www", "foo.ihopethiswillneverbeapublicsuffix", "x.y.z");

  /**