IMO Shortlist 1979 problem 16


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2. travnja 2012.
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Let K denote the set \{a, b, c, d, e\}. F is a collection of 16 different subsets of K, and it is known that any three members of F have at least one element in common. Show that all 16 members of F have exactly one element in common.
Izvor: Međunarodna matematička olimpijada, shortlist 1979