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kn points of plane, k given colors, n points of each color

Source: Rioplatense 1998 L3 P6

September 19, 2022
geometrypointscombinatorial geometry

Problem Statement

Let kk be a fixed positive integer. For each n=1,2,...,n = 1, 2,..., we will call configuration of order nn any set of knkn points of the plane, which does not contain 33 collinear, colored with kk given colors, so that there are nn points of each color. Determine all positive integers nn with the following property: in each configuration of order nn, it is possible to select three points of each color, such that the kk triangles with vertices of the same color that are determined are disjoint in pairs.