@Override
	Set<List<E>> words() {
		Set<List<E>> res = new HashSet<>();
		if (!correct()) {
			return res;
		}
		for(List<E> word1: left.words()) {
			for (List<E> word2 : right.words()) {
				List<E> word1_copy = new ArrayList<>(word1);
				word1.addAll(word2);
				word2.addAll(word1_copy);
				res.add(word1);
				res.add(word2);

				//res.add(Stream.concat(word1.stream(), word2.stream()).collect(Collectors.toList()));
				//res.add(Stream.concat(word2.stream(), word1.stream()).collect(Collectors.toList()));
			}
		}
		return res;
	}