}
  }

  /**
   * Called by the default implementation of {@link #subList} when {@code toIndex - fromIndex > 1},
   * after index validation has already been performed.
   */
  ImmutableList<E> subListUnchecked(int fromIndex, int toIndex) {
    return new SubList(fromIndex, toIndex - fromIndex);
  }

  class SubList extends ImmutableList<E> {
    final transient int offset;
    final transient int length;

    }
  }

  /**
   * Called by the default implementation of {@link #subList} when {@code toIndex - fromIndex > 1},
   * after index validation has already been performed.
   */
  ImmutableList<E> subListUnchecked(int fromIndex, int toIndex) {
    return new SubList(fromIndex, toIndex - fromIndex);
  }

  class SubList extends ImmutableList<E> {
    final transient int offset;
    final transient int length;

  }

  public static <E> ImmutableList<E> copyOf(Collection<? extends E> elements) {
    if (elements instanceof ImmutableCollection) {
      /*
       * TODO: When given an ImmutableList that's a sublist, copy the referenced
       * portion of the array into a new array to save space?
       */
      @SuppressWarnings("unchecked") // all supported methods are covariant