return new RegularImmutableList<E>(ImmutableList.<E>nullCheckedList(e1, e2));
  }

  public static <E> ImmutableList<E> of(E e1, E e2, E e3) {
    return new RegularImmutableList<E>(ImmutableList.<E>nullCheckedList(e1, e2, e3));
  }

  public static <E> ImmutableList<E> of(E e1, E e2, E e3, E e4) {
    return new RegularImmutableList<E>(ImmutableList.<E>nullCheckedList(e1, e2, e3, e4));
  }