

ITA Software: General air travel search is undecidable - gruseom
http://research.swtch.com/2008/02/traveling-passenger-problems.html

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xirium
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> ).

