From the article: "The question of whether a valid ticket exists can not be solved for all databases and all queries no matter how long a computer thinks." Be

From the article: "The question of whether a valid ticket exists can not be solved for all databases and all queries no matter how long a computer thinks." Be very concerned if a flight reservation system offers you a room in the Hilbert Hotel ( http://en.wikipedia.org/wiki/Hilbert_Hotel http://en.wikipedia.org/wiki/Hilbert_Hotel ).