Suppose a friend of yours is rushing for one of the university fraternities, Tau Nu Tau (TNT). His job for this week is to arrange all the bottles in the TNT beerbottle collection in a circle, subject to the constraint that each pair of consecutive bottles must be for beers that were both drunk in some TNT party. He has been given a listing of the beers in the TNT beer-bottle collection, and, for each beer on the list, he is told which other beers were drunk along with this one at some TNT party. Politely show that your friend has been asked to solve an NP-complete problem.