3 Search Results for "Rey, Anja"

Document
DOI: 10.4230/LIPIcs.AFT.2025.21
Pool Formation in Oceanic Games: Shapley Value and Proportional Sharing

Authors: Aggelos Kiayias, Elias Koutsoupias, Evangelos Markakis, and Panagiotis Tsamopoulos

Published in: LIPIcs, Volume 354, 7th Conference on Advances in Financial Technologies (AFT 2025)

Abstract
We study a game-theoretic model for pool formation in Proof of Stake blockchain protocols. In such systems, stakeholders can form pools as a means of obtaining regular rewards from participation in ledger maintenance, with the power of each pool being dependent on its collective stake. The question we are interested in is the design of mechanisms, i.e., "reward sharing schemes," that suitably split rewards among pool members and achieve favorable properties in the resulting pool configuration. With this in mind, we initiate a non-cooperative game-theoretic analysis of the well known Shapley value scheme from cooperative game theory into the context of blockchains. In particular, we focus on the oceanic model of games, proposed by Milnor and Shapley (1978), which is suitable for populations where a small set of large players coexists with a big mass of rather small, negligible players. This provides an appropriate level of abstraction for pool formation processes that occur among the stakeholders of a blockchain. We provide comparisons between the Shapley mechanism and the more standard proportional scheme, in terms of attained decentralization, via a Price of Stability analysis and in terms of susceptibility to Sybil attacks, i.e., the strategic splitting of a players' stake with the intention of participating in multiple pools for increased profit. Interestingly, while the widely deployed proportional scheme appears to have certain advantages, the Shapley value scheme, which rewards higher the most pivotal players, emerges as a competitive alternative, by being able to bypass some of the downsides of proportional sharing in terms of Sybil attack susceptibility, while also not being far from optimal guarantees w.r.t. decentralization. Finally, we also complement our study with some variations of proportional sharing, where the profit is split in proportion to a superadditive or a subadditive function of the stake, showing that our results for the Shapley value scheme are maintained in comparison to these functions as well.
Cite as

Aggelos Kiayias, Elias Koutsoupias, Evangelos Markakis, and Panagiotis Tsamopoulos. Pool Formation in Oceanic Games: Shapley Value and Proportional Sharing. In 7th Conference on Advances in Financial Technologies (AFT 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 354, pp. 21:1-21:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{kiayias_et_al:LIPIcs.AFT.2025.21,
  author =	{Kiayias, Aggelos and Koutsoupias, Elias and Markakis, Evangelos and Tsamopoulos, Panagiotis},
  title =	{{Pool Formation in Oceanic Games: Shapley Value and Proportional Sharing}},
  booktitle =	{7th Conference on Advances in Financial Technologies (AFT 2025)},
  pages =	{21:1--21:24},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-400-0},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{354},
  editor =	{Avarikioti, Zeta and Christin, Nicolas},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.AFT.2025.21},
  URN =		{urn:nbn:de:0030-drops-247409},
  doi =		{10.4230/LIPIcs.AFT.2025.21},
  annote =	{Keywords: Shapley value, Nash equilibria, Price of Stability, Reward sharing schemes, Proof of Stake blockchains}
}
Document
DOI: 10.4230/DagRep.11.7.1
Coalition Formation Games (Dagstuhl Seminar 21331)

Authors: Edith Elkind, Judy Goldsmith, Anja Rey, and Jörg Rothe

Published in: Dagstuhl Reports, Volume 11, Issue 7 (2021)

Abstract
There are many situations in which individuals will choose to act as a group, or coalition. Examples include social clubs, political parties, partnership formation, and legislative voting. Coalition formation games are a class of cooperative games where the aim is to partition a set of agents into coalitions, according to some criteria, such as coalitional stability or maximization of social welfare. In our seminar we discussed applications, results, and new directions of research in the field of coalition formation games.
Cite as

Edith Elkind, Judy Goldsmith, Anja Rey, and Jörg Rothe. Coalition Formation Games (Dagstuhl Seminar 21331). In Dagstuhl Reports, Volume 11, Issue 7, pp. 1-15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@Article{elkind_et_al:DagRep.11.7.1,
  author =	{Elkind, Edith and Goldsmith, Judy and Rey, Anja and Rothe, J\"{o}rg},
  title =	{{Coalition Formation Games (Dagstuhl Seminar 21331)}},
  pages =	{1--15},
  journal =	{Dagstuhl Reports},
  ISSN =	{2192-5283},
  year =	{2021},
  volume =	{11},
  number =	{7},
  editor =	{Elkind, Edith and Goldsmith, Judy and Rey, Anja and Rothe, J\"{o}rg},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagRep.11.7.1},
  URN =		{urn:nbn:de:0030-drops-155885},
  doi =		{10.4230/DagRep.11.7.1},
  annote =	{Keywords: Coalition Formation, Cooperative Games}
}
Document
DOI: 10.4230/LIPIcs.MFCS.2016.80
Structural Control in Weighted Voting Games

Authors: Anja Rey and Jörg Rothe

Published in: LIPIcs, Volume 58, 41st International Symposium on Mathematical Foundations of Computer Science (MFCS 2016)

Abstract
Inspired by the study of control scenarios in elections and complementing manipulation and bribery settings in cooperative games with transferable utility, we introduce the notion of structural control in weighted voting games. We model two types of influence, adding players to and deleting players from a game, with goals such as increasing a given player's Shapley-Shubik or probabilistic Penrose-Banzhaf index in relation to the original game. We study the computational complexity of the problems of whether such structural changes can achieve the desired effect.
Cite as

Anja Rey and Jörg Rothe. Structural Control in Weighted Voting Games. In 41st International Symposium on Mathematical Foundations of Computer Science (MFCS 2016). Leibniz International Proceedings in Informatics (LIPIcs), Volume 58, pp. 80:1-80:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2016)

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@InProceedings{rey_et_al:LIPIcs.MFCS.2016.80,
  author =	{Rey, Anja and Rothe, J\"{o}rg},
  title =	{{Structural Control in Weighted Voting Games}},
  booktitle =	{41st International Symposium on Mathematical Foundations of Computer Science (MFCS 2016)},
  pages =	{80:1--80:15},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-016-3},
  ISSN =	{1868-8969},
  year =	{2016},
  volume =	{58},
  editor =	{Faliszewski, Piotr and Muscholl, Anca and Niedermeier, Rolf},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2016.80},
  URN =		{urn:nbn:de:0030-drops-64883},
  doi =		{10.4230/LIPIcs.MFCS.2016.80},
  annote =	{Keywords: algorithmic games theory, weighted voting games, structural control, power indices, computational complexity}
}
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