code: public static <K, V> ImmutableBiMap<K, V> of(K k1, V v1, K k2, V v2) {
      return RegularImmutableBiMap.fromEntries(entryOf(k1, v1), entryOf(k2, v2));
    }
docs: Returns an immutable map containing the given entries, in order.
  
  @throws IllegalArgumentException if duplicate keys or values are added