private final transient @Nullable Object keyHashTable;
  @VisibleForTesting final transient @Nullable Object[] alternatingKeysAndValues;
  private final transient int keyOffset; // 0 for K-to-V, 1 for V-to-K
  private final transient int size;
  private final transient RegularImmutableBiMap<V, K> inverse;

  /** Constructor for empty bimap. */

  // The first `size` elements are non-null.
  @VisibleForTesting final transient @Nullable Object[] elements;
  private final transient int hashCode;
  // the same values as `elements` in hashed positions (plus nulls)
  @VisibleForTesting final transient @Nullable Object[] table;
  // 'and' with an int to get a valid table index.
  private final transient int mask;
  private final transient int size;

  RegularImmutableSet(

 */
@GwtCompatible
@SuppressWarnings("serial") // uses writeReplace(), not default serialization
final class SingletonImmutableBiMap<K, V> extends ImmutableBiMap<K, V> {

  final transient K singleKey;
  final transient V singleValue;

  SingletonImmutableBiMap(K singleKey, V singleValue) {
    checkEntryNotNull(singleKey, singleValue);
    this.singleKey = singleKey;
    this.singleValue = singleValue;

                true), RESOURCE_LOCKED("Resource is locked", ErrorCategory.RESOURCE, true),

        // Transient errors
        BUSY("Server busy", ErrorCategory.TRANSIENT, true), TRY_AGAIN("Try again later", ErrorCategory.TRANSIENT,
                true), SERVICE_UNAVAILABLE("Service temporarily unavailable", ErrorCategory.TRANSIENT, true),

        // Generic errors

    }
  }

  abstract Iterator<Entry<K, V>> entryIterator();

  @LazyInit private transient @Nullable Set<K> keySet;

  @Override
  public Set<K> keySet() {
    Set<K> result = keySet;
    return (result == null) ? keySet = createKeySet() : result;
  }

  abstract Set<K> createKeySet();

  @LazyInit private transient @Nullable Multiset<K> keys;

  @Override
  public Multiset<K> keys() {

  /** Maps an "entry" to the key of that entry. */
  private transient @Nullable K[] keys;

  /** Maps an "entry" to the value of that entry. */
  private transient @Nullable V[] values;

  private transient int size;
  private transient int modCount;

  /** Maps a bucket to the "entry" of its first element. */
  private transient int[] hashTableKToV;

  /** Maps a bucket to the "entry" of its first element. */

   * by init(), which the constructor calls.
   */

  /** The keys of the entries in the map. */
  transient @Nullable Object[] keys;

  /** The values of the entries in the map. */
  transient int[] values;

  transient int size;

  transient int modCount;

  /**
   * The hashtable. Its values are indexes to the keys, values, and entries arrays.
   *

  }

  static final class EntrySet<K, V> extends ImmutableSet<Entry<K, V>> {
    private final transient ImmutableMap<K, V> map;
    private final transient @Nullable Object[] alternatingKeysAndValues;
    private final transient int keyOffset;
    private final transient int size;

    EntrySet(
        ImmutableMap<K, V> map,
        @Nullable Object[] alternatingKeysAndValues,

   */
  @VisibleForTesting static final int MAX_HASH_BUCKET_LENGTH = 9;

  private final transient ImmutableEntry<E>[] entries;
  private final transient @Nullable ImmutableEntry<?>[] hashTable;
  private final transient int size;
  private final transient int hashCode;

  @LazyInit private transient @Nullable ImmutableSet<E> elementSet;

  private RegularImmutableMultiset(
      ImmutableEntry<E>[] entries,

      new RegularImmutableSet<>(EMPTY_ARRAY, 0, EMPTY_ARRAY, 0);

  private final transient Object[] elements;
  private final transient int hashCode;
  // the same values as `elements` in hashed positions (plus nulls)
  @VisibleForTesting final transient @Nullable Object[] table;
  // 'and' with an int to get a valid table index.
  private final transient int mask;