Unimodality and equivalence of simple and coalitional strategy-proofness in convex idempotent interval spaces
Stefano Vannucci · RePEc: Research Papers in Economics · 2012
It is shown that simple and coalitional strategy-proofness of a voting rule as defi?ned on the full unimodal domain of a convex idempotent interval space (X; I) are equivalent properties if (X; I) satis?es interval anti-exchange, a basic property also shared by a large class of convex geometries including -but not reducing to- trees and linear geometries. Therefore, strategy-proof location problems in a vast class of networks fall under the scope of that statement. It is also established that a much weaker minimal anti-exchange property is necessary to ensure equivalence of simple and coalitional strategy-proofness in that setting. An immediate corollary to that result is that such ?unimodal?equivalence fails to hold both in certan median interval spaces including those induced by bounded median semilattices that are not chains, and in certain non-median interval spaces including those induced by Hamming graphs and partial cubes.