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Is having a unique equilibrium robust?

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  • Viossat, Yannick

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

  • Viossat, Yannick, 2008. "Is having a unique equilibrium robust?," Journal of Mathematical Economics, Elsevier, vol. 44(11), pages 1152-1160, December.
    • Handle: RePEc:eee:mateco:v:44:y:2008:i:11:p:1152-1160
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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. Viossat, Yannick, 2008. "Evolutionary dynamics may eliminate all strategies used in correlated equilibrium," Mathematical Social Sciences, Elsevier, vol. 56(1), pages 27-43, July.
    4. 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.
    5. Kevin He & Fedor Sandomirskiy & Omer Tamuz, 2021. "Private Private Information," Papers 2112.14356, arXiv.org, revised Sep 2024.
    6. Lehrer, Ehud & Solan, Eilon & Viossat, Yannick, 2011. "Equilibrium payoffs of finite games," Journal of Mathematical Economics, Elsevier, vol. 47(1), pages 48-53, January.

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