class PartialOrderedSet extends HashSet<E> {

	@Override
	public boolean removeIf(final Predicate<? super E> filter) {
		Objects.requireNonNull(filter);
		boolean removed = false;
		final Iterator<E> each = this.order.keySet().iterator();
		while (each.hasNext()) {
			E next = each.next();
			if (filter.test(next)) {
				this.remove(next);
				removed = true;
			}
		}
		return removed;
	}

	public  PartialOrderedSet(final PartialOrderedSet<E> original);
	public  PartialOrderedSet();

}