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MathNet 2023-part-03 — 191 problems (EN–VI) Question 40

Math Olympiad Vault · MathNet 2023-part-03 — 191 problems (EN–VI)

Question 40

The game of **Hive** is played on a regular hexagonal grid (as shown in the figure) by 3 players. The grid consists of $k$ layers (where $k$ is a natural number) surrounding a regular hexagon, with each layer constructed around the previous layer. The figure below shows a grid with 2 layers.

The players, *Ali*, *Shayan*, and *Sajad*, take turns playing the game. In each turn, a player places a tile, similar to the one shown in the figure, on the empty cells of the grid (rotation of the tile is also allowed). The first player who is unable to place a tile on the grid loses the game. Prove that two players can collaborate in such a way that the third player always loses.

Question illustration

Question illustration