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IMO ShortList 1998, combinatorics theory problem 6

Source: IMO ShortList 1998, combinatorics theory problem 6

October 22, 2004
combinatoricspoint setcombinatorial geometryColoringIMO Shortlist

Problem Statement

Ten points are marked in the plane so that no three of them lie on a line. Each pair of points is connected with a segment. Each of these segments is painted with one of kk colors, in such a way that for any kk of the ten points, there are kk segments each joining two of them and no two being painted with the same color. Determine all integers kk, 1k101\leq k\leq 10, for which this is possible.