On Avoider-Enforcer games

Abstract

In the Avoider-Enforcer game on the complete graph $K_n$, the players (Avoider and Enforcer) each take an edge in turn. Given a graph property $\mathcal{P}$, Enforcer wins the game if Avoider's graph has the property $\mathcal{P}$. An important parameter is $τ_E({\cal P})$, the smallest integer $t$ such that Enforcer can win the game against any opponent in $t$ rounds. In this paper, let $\mathcal{F}$ be an arbitrary family of graphs and $\mathcal{P}$ be the property that a member of $\mathcal{F}$ is a subgraph or is an induced subgraph. We determine the asymptotic value of $τ_E(\mathcal{P})$ when $\mathcal{F}$ contains no bipartite graph and establish that $τ_E(\mathcal{P})=o(n^2)$ if $\mathcal{F}$ contains a bipartite graph. The proof uses the game of JumbleG and the Szemerédi Regularity Lemma.