Maths Olympiad Prep

Track / Stage 7 / 3 of 300 #1403 of 1964

Problem 1403

National Olympiad second round; IMO P1/P4
Combinatorics Difficulty 7.0 Prove it KöMaL 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 AZA \subset \mathbb{Z} there exists kZk\in \mathbb{Z} such that the point (x,k)(x,k) is colored red if and only if xAx\in A.

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