English

Strong Ramsey Games: Drawing on an infinite board

Combinatorics 2016-05-26 v2

Abstract

We consider the strong Ramsey-type game R(k)(H,0)\mathcal{R}^{(k)}(\mathcal{H}, \aleph_0), played on the edge set of the infinite complete kk-uniform hypergraph KNkK^k_{\mathbb{N}}. Two players, called FP (the first player) and SP (the second player), take turns claiming edges of KNkK^k_{\mathbb{N}} with the goal of building a copy of some finite predetermined kk-uniform hypergraph H\mathcal{H}. The first player to build a copy of H\mathcal{H} wins. If no player has a strategy to ensure his win in finitely many moves, then the game is declared a draw. In this paper, we construct a 55-uniform hypergraph H\mathcal{H} such that R(5)(H,0)\mathcal{R}^{(5)}(\mathcal{H}, \aleph_0) is a draw. This is in stark contrast to the corresponding finite game R(5)(H,n)\mathcal{R}^{(5)}(\mathcal{H}, n), played on the edge set of Kn5K^5_n. Indeed, using a classical game-theoretic argument known as \emph{strategy stealing} and a Ramsey-type argument, one can show that for every kk-uniform hypergraph G\mathcal{G}, there exists an integer n0n_0 such that FP has a winning strategy for R(k)(G,n)\mathcal{R}^{(k)}(\mathcal{G}, n) for every nn0n \geq n_0.

Keywords

Cite

@article{arxiv.1605.05443,
  title  = {Strong Ramsey Games: Drawing on an infinite board},
  author = {Dan Hefetz and Christopher Kusch and Lothar Narins and Alexey Pokrovskiy and Clément Requilé and Amir Sarid},
  journal= {arXiv preprint arXiv:1605.05443},
  year   = {2016}
}

Comments

16 pages, updated introduction and references; improved figure