Requirements on the social choice function (2/2)

4) Independence of irrelevant alternatives

The group’s choice doesn’t change if we add an alternative that is

• Considered inferior to all other alternatives by all DMs, or
• Is a copy of an existing alternative

5) Pareto principle

If all group members prefer x to y, the group should choose the alternative x

6) Non dictatorship

There is no DMi such that x Ri y ? x R y

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