English

A counterexample to conjecture "Catch 22"

Combinatorics 2024-12-24 v2

Abstract

We construct a finite deterministic graphical (DG) game without Nash equilibria in pure stationary strategies. This game has 3 players I={1,2,3}I=\{1,2,3\} and 5 outcomes: 2 terminal a1a_1 and a2a_2 and 3 cyclic. Furthermore, for 2 players a terminal outcome is the best: a1a_1 for player 3 and a2a_2 for player 1. Hence, the rank vector rr is at most (1,2,1)(1,2,1). Here rir_i is the number of terminal outcomes that are worse than some cyclic outcome for the player iIi \in I. This is a counterexample to conjecture ``Catch 22" from the paper ``On Nash-solvability of finite nn-person DG games, Catch 22" (2021) arXiv:2111.06278, according to which, at least 2 entries of rr are at least 2 for any NE-free game. However, Catch 22 remains still open for the games with a unique cyclic outcome, not to mention a weaker (and more important) conjecture claiming that an nn-person finite DG game has a Nash equilibrium (in pure stationary strategies) when r=(0n)r = (0^n), that is, all nn entries of rr are 0; in other words, when the following condition holds: \qquad\bullet (C0C_0) any terminal outcome is better than every cyclic one for each player. A game is play-once if each player controls a unique position. It is known that any play-once game satisfying (C0C_0) has a Nash equilibrium. We give a new and very short proof of this statement. Yet, not only conjunction but already disjunction of the above two conditions may be sufficient for Nash-solvability. This is still open.

Keywords

Cite

@article{arxiv.2406.14587,
  title  = {A counterexample to conjecture "Catch 22"},
  author = {Bogdan Butyrin and Vladimir Gurvich and Anton Lutsenko and Mariya Naumova and Maxim Peskin},
  journal= {arXiv preprint arXiv:2406.14587},
  year   = {2024}
}
R2 v1 2026-06-28T17:13:51.870Z