return CollectSpliterators.filter(unfiltered.spliterator(), predicate);
    }

    @Override
    public void forEach(Consumer<? super E> action) {
      checkNotNull(action);
      unfiltered.forEach(
          (E e) -> {
            if (predicate.test(e)) {
              action.accept(e);
            }
          });
    }

    @Override
    public boolean remove(@CheckForNull Object element) {

   *
   * <p><i>Notes:</i> This is an implementation of the algorithm for Lexicographical Permutations
   * Generation, described in Knuth's "The Art of Computer Programming", Volume 4, Chapter 7,
   * Section 7.2.1.2. The iteration order follows the lexicographical order. This means that the
   * first permutation will be in ascending order, and the last will be in descending order.
   *