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On sustainable equilibria

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  • Govindan, Srihari
  • Laraki, Rida
  • Pahl, Lucas

Abstract

Following the ideas laid out in Myerson (1996), Hofbauer (2003) defined a Nash equilibrium of a finite game as sustainable if it can be made the unique Nash equilibrium of a game obtained by deleting/adding a subset of the strategies that are inferior replies to it. This paper proves a result about sustainable equilibria and uses it to provide a refinement as well. Our result concerns the Hofbauer-Myerson conjecture about the relationship between the sustainability of an equilibrium and its index: for a generic class of games, an equilibrium is sustainable iff its index is +1. von Schemde and von Stengel (2008) proved this conjecture for bimatrix games; we show that the conjecture is true for all finite games. More precisely, we prove that an equilibrium is isolated and has index +1 if and only if it can be made unique in a larger game obtained by adding finitely many strategies that are inferior replies to that equilibrium. It follows in a straightforward way from our result that sustainable equilibria fail the Decomposition Axiom for games as formulated by Mertens (1989a). In order to rectify this problem we propose a refinement, called strongly sustainable equilibria, which is shown to exist for all regular games.

Suggested Citation

  • Govindan, Srihari & Laraki, Rida & Pahl, Lucas, 2023. "On sustainable equilibria," Journal of Economic Theory, Elsevier, vol. 213(C).
    • Handle: RePEc:eee:jetheo:v:213:y:2023:i:c:s0022053123001321
    DOI: 10.1016/j.jet.2023.105736
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    References listed on IDEAS

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    More about this item

    Keywords

    Sustainable equilibria; Index of equilibria; Refinements of equilibria;
    All these keywords.

    JEL classification:

    • C02 - Mathematical and Quantitative Methods - - General - - - Mathematical Economics
    • C72 - Mathematical and Quantitative Methods - - Game Theory and Bargaining Theory - - - Noncooperative Games

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