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N point on a circle

Source: 17-th Iranian Mathematical Olympiad 1999/2000

December 14, 2005
combinatorics proposedcombinatorics

Problem Statement

Let nn points be given on a circle, and let nk+1nk + 1 chords between these points be drawn, where 2k+1<n2k+1 < n. Show that it is possible to select k+1k+1 of the chords so that no two of them intersect.