The Real Computational Complexity of Minmax Value and Equilibrium Refinements in Multi-player Games

Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 10504)


We show that for several solution concepts for finite n-player games, where \(n \ge 3\), the task of simply verifying its conditions is computationally equivalent to the decision problem of the existential theory of the reals. This holds for trembling hand perfect equilibrium, proper equilibrium, and CURB sets in strategic form games and for (the strategy part of) sequential equilibrium, trembling hand perfect equilibrium, and quasi-perfect equilibrium in extensive form games. For obtaining these results we first show that the decision problem for the minmax value in n-player games, where \(n\ge 3\), is also equivalent to the decision problem for the existential theory of the reals.

Our results thus improve previous results of \(\mathrm {NP}\)-hardness as well as \(\textsc {Sqrt-Sum}\)-hardness of the decision problems to completeness for \(\exists \mathbb {R}\), the complexity class corresponding to the decision problem of the existential theory of the reals. As a byproduct we also obtain a simpler proof of a result by Schaefer and Štefankovič giving \(\exists \mathbb {R}\)-completeness for the problem of deciding existence of a probability constrained Nash equilibrium.


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© Springer International Publishing AG 2017

Authors and Affiliations

  1. 1.Aarhus UniversityAarhusDenmark

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