A counterexample to conjecture "Catch 22"
Abstract
We construct a finite deterministic graphical (DG) game without Nash equilibria in pure stationary strategies. This game has 3 players and 5 outcomes: 2 terminal and and 3 cyclic. Furthermore, for 2 players a terminal outcome is the best: for player 3 and for player 1. Hence, the rank vector is at most . Here is the number of terminal outcomes that are worse than some cyclic outcome for the player . This is a counterexample to conjecture ``Catch 22" from the paper ``On Nash-solvability of finite -person DG games, Catch 22" (2021) arXiv:2111.06278, according to which, at least 2 entries of 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 -person finite DG game has a Nash equilibrium (in pure stationary strategies) when , that is, all entries of are 0; in other words, when the following condition holds: () 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 () 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.
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}
}