CombinatoricsDifficulty 7.0Prove itKöMaL problem A · Hungary · 2022
Some lattice points in the Cartesian coordinate system are colored red, the rest of the lattice points are colored blue. Such a coloring is called finitely universal, if for any finite, non-empty A⊂Z there exists k∈Z such that the point (x,k) is colored red if and only if x∈A.
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