3ThelatterfollowsegfromtheundecidabilityofbagcontainmentofunionsofconjunctivequeriesUCQs21sinceforUCQsQQ0wehaveQiscontainedinQ0iQQ0isequivalenttotheemptyanswerqueryThemaincontributionso ID: 411707
3Thelatterfollows e.g. fromtheundecidabilityofbag-containmentofunionsofconjunctivequeries(UCQs)[21]