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Is Having a Unique Equilibrium Robust?

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  • Yannick Viossat

    (CEREMADE - CEntre de REcherches en MAthématiques de la DEcision - Université Paris Dauphine-PSL - PSL - Université Paris Sciences et Lettres - CNRS - Centre National de la Recherche Scientifique)

Abstract

We investigate whether having a unique equilibrium (or a given number of equilibria) is robust to perturbation of the payoffs, both for Nash equilibrium and correlated equilibrium. We show that the set of n-player finite games with a unique correlated equilibrium is open, while this is not true of Nash equilibrium for n>2. The crucial lemma is that a unique correlated equilibrium is a quasi-strict Nash equilibrium. Related results are studied. For instance, we show that generic two-person zero-sum games have a unique correlated equilibrium and that, while the set of symmetric bimatrix games with a unique symmetric Nash equilibrium is not open, the set of symmetric bimatrix games with a unique and quasi-strict symmetric Nash equilibrium is.

Suggested Citation

  • Yannick Viossat, 2008. "Is Having a Unique Equilibrium Robust?," Post-Print hal-00361891, HAL.
    • Handle: RePEc:hal:journl:hal-00361891
    DOI: 10.1016/j.jmateco.2007.06.008
    Note: View the original document on HAL open archive server: https://hal.science/hal-00361891
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    8. Forges, Francoise, 1990. "Correlated Equilibrium in Two-Person Zero-Sum Games," Econometrica, Econometric Society, vol. 58(2), pages 515-515, March.
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    Cited by:

    1. Ezra Einy & Ori Haimanko & David Lagziel, 2022. "Strong robustness to incomplete information and the uniqueness of a correlated equilibrium," Economic Theory, Springer;Society for the Advancement of Economic Theory (SAET), vol. 73(1), pages 91-119, February.
    2. Yannick Viossat, 2010. "Properties and applications of dual reduction," Economic Theory, Springer;Society for the Advancement of Economic Theory (SAET), vol. 44(1), pages 53-68, July.
    3. Kevin He & Fedor Sandomirskiy & Omer Tamuz, 2021. "Private Private Information," Papers 2112.14356, arXiv.org, revised Jun 2023.
    4. Viossat, Yannick, 2008. "Evolutionary dynamics may eliminate all strategies used in correlated equilibrium," Mathematical Social Sciences, Elsevier, vol. 56(1), pages 27-43, July.
    5. Lehrer, Ehud & Solan, Eilon & Viossat, Yannick, 2011. "Equilibrium payoffs of finite games," Journal of Mathematical Economics, Elsevier, vol. 47(1), pages 48-53, January.
    6. Klis Anna A., 2019. "On the Openness of Unique Pure-Strategy Nash Equilibrium," The B.E. Journal of Theoretical Economics, De Gruyter, vol. 19(1), pages 1-9, January.

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