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Multiagent Systems

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Prof. Dr. Jürgen Dix · Department of Informatics, TUC <strong>Multiagent</strong> <strong>Systems</strong>, WS 06/07 284/731<br />

4. Decision Making (2) 1. Voting<br />

Theorem 4.11 (Arrow (1951))<br />

If the social welfare function f ∗ is (1) pareto efficient and (2)<br />

independent from irrelevant alternatives, then there always<br />

exists a dictator: for all U ⊆ ∏ |A|<br />

Ordpar<br />

∃i ∈ A : ∀o, o ′ ∈ O : o≺ i o ′<br />

To be more precise: for all U ⊆ ∏ |A|<br />

i=1 Ord<br />

iff o≺ ≺ ∗ o ′ .<br />

Ord<br />

i=1 Ordpar<br />

∃i ∈ A : ∀〈≺ 1 , . . . , ≺ |A| 〉 ∈ U :<br />

∀o, o ′ ∈ O, o≺ i o ′ iff o f ∗ (〈≺ 1 , . . . , ≺ |A| 〉) o ′ .

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