IMO Shortlist 2002 problem C5


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2. travnja 2012.
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Let r\geq2 be a fixed positive integer, and let F be an infinite family of sets, each of size r, no two of which are disjoint. Prove that there exists a set of size r-1 that meets each set in F.
Izvor: Međunarodna matematička olimpijada, shortlist 2002