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834. Strategy-Proof Aggregation Rules in Median Join-Semilattices and Arrowian Social Welfare Functions

Working Paper n.834 - Luglio 2020

Ernesto Savaglio

DEC, University of Pescara, Italy

Stefano Vannucci

DEPS, USiena


Three characterizations of the whole class of strategy-proof aggregation rules on rich domains of locally unimodal total preorders in finite median join-semilattices are provided. In particular, it is shown that such class consists precisely of generalized weak consensus-sponsorship rules induced by certain families of order filters of the coalition poset. It follows that the co-majority rule and many other inclusive aggregation rules belong to that class. The co-majority rule for an odd number of agents is also characterized. The existence of strategy-proof anonymous neutral and unanimity-respecting social welfare functions which satisfy a suitably relaxed independence condition is shown to follow from our characterizations.
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