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

  /*
   * This could have a good default implementation of return new ImmutableKeySet<K, V>(this),
   * but ProGuard can't figure out how to eliminate that default when RegularImmutableMap
   * overrides it.
   */
  abstract ImmutableSet<K> createKeySet();

    // when deep chains of futures exist resulting in a StackOverflowException. We could detect
    // arbitrary cycles using a thread local but this should be a good enough solution (it is also
    // what jdk collections do in these cases)
    try {
      if (o == this) {
        builder.append("this future");
      } else {
        builder.append(o);
      }

        return this.bimap.equals(that.bimap);
      }
      return false;
    }

    @Override
    public int hashCode() {
      return bimap.hashCode();
    }

    // There's really no good way to implement toString() without printing the entire BiMap, right?
    @Override
    public String toString() {
      return "Maps.asConverter(" + bimap + ")";
    }