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The limits of ex post implementation

Jehiel, P.; Meyer-ter-Vehn, M.; Moldovanu, B.; Zame, B.; (2006) The limits of ex post implementation. (ELSE Working Papers 183). ESRC Centre for Economic Learning and Social Evolution: London, UK. Green open access


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The sensitivity of Bayesian implementation to agents' beliefs about others suggests the use of more robust notions of implementation such as ex-post implementation, which requires that each agent' s strategy be optimal for every possible realization of the types of other agents. We show that the only deterministic social choice functions that are ex-post implementable in generic mechanism design frameworks with multi-dimensional signals, interdependent valuations and transferable utilities, are constant functions. In other words, deterministic ex-post implementation requires that the same alternative must be chosen irrespective of agents' signals. The proof shows that ex-post implementability of a non-trivial deterministic social choice function implies that certain rates of information substitution coincide for all agents. This condition amounts to a system of differential equations that are not satis�ed by generic valuation functions.

Type: Working / discussion paper
Title: The limits of ex post implementation
Open access status: An open access version is available from UCL Discovery
Publisher version: http://else.econ.ucl.ac.uk/newweb/papers.php#2006
Language: English
UCL classification: UCL > Provost and Vice Provost Offices > UCL SLASH > Faculty of S&HS > Dept of Economics
URI: https://discovery.ucl.ac.uk/id/eprint/14540
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