Group Obvious Strategy-proofness: Definition and Characterization

• Authors: Alejandro Neme, R. Pablo Arribillaga and Jordi Massó.
• BSE Working Paper: 1533 | November 25
• Keywords: obvious strategy-proofness , (group) strategy-proofness
• JEL codes: D71

We introduce the concept of group obvious strategy-proofness, an extension of Li (2017)’s notion of obvious strategy-proofness, by requiring that truth-telling re- mains an obviously dominant strategy for any group of agents in the extensive game form implementing the social choice function. We show that this stronger condition is no more restrictive: the set of all group obviously strategy-proof social choice functions coincides with the set of all obviously strategy-proof social choice functions. Building on this equivalence result and on existing results on obvious strategy-proofness via extensive game forms with perfect information, we derive additional equivalences concerning the implementability of social choice functions: in this class of games, strategy-proofness, group strategy-proofness, obvious strategy-proofness, and group obvious strategy-proofness are all equivalent.