Problem A. 531. (March 2011)
A. 531. Prove that for every positive integer k there is a positive integer N_{k} (depending only on k) such that whenever is a set system whose elements are at most kelement sets such that every two elements of have an element in common, then there exists a set A with at most N_{k} elements such that every two elements of and A have an element in common.
(Proposed by: Ambrus Zsbán, Budapest)
(5 pont)
Deadline expired on 11 April 2011.
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