public static <K, V> ImmutableMap<K, V> of() {
    return (ImmutableMap<K, V>) RegularImmutableMap.EMPTY;
  }

  public static <K, V> ImmutableMap<K, V> of(K k1, V v1) {
    return ImmutableBiMap.of(k1, v1);
  }

  public static <K, V> ImmutableMap<K, V> of(K k1, V v1, K k2, V v2) {
    return new RegularImmutableMap<K, V>(entryOf(k1, v1), entryOf(k2, v2));
  }

    return RegularImmutableMap.fromEntries(entryOf(k1, v1), entryOf(k2, v2));
  }

  /**
   * Returns an immutable map containing the given entries, in order.
   *
   * @throws IllegalArgumentException if duplicate keys are provided
   */
  public static <K, V> ImmutableMap<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3) {