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Abstract: We study the control complexity of fallback voting. Like manipulation andbribery, electoral control describes ways of changing the outcome of anelection; unlike manipulation or bribery attempts, control actions-such asadding-deleting-partitioning either candidates or voters-modify theparticipative structure of an election. Via such actions one can try to eithermake a favorite candidate win -constructive control- or prevent a despisedcandidate from winning -destructive control-. Computational complexity can beused to protect elections from control attempts, i.e., proving an electionsystem resistant to some type of control shows that the success of thecorresponding control action, though not impossible, is computationallyprohibitive. We show that fallback voting, an election system combiningapproval with majority voting, is resistant to each of the common types ofcandidate control and to each common type of constructive control. Amongnatural election systems with a polynomial-time winner problem, only pluralityand sincere-strategy preference-based approval voting SP-AV were previouslyknown to be fully resistant to candidate control, and only Copeland voting andSP-AV were previously known to be fully resistant to constructive control.However, plurality has fewer resistances to voter control, Copeland voting hasfewer resistances to destructive control, and SP-AV which like fallback votinghas 19 out of 22 proven control resistances is arguably less natural a systemthan fallback voting.



Author: Gábor Erdélyi, Lena Piras, Jörg Rothe

Source: https://arxiv.org/



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