Tournaments determined by three and five voters
Abstract
The Kemeny median problem asks for a linear order minimizing the total pairwise disagreement with given rankings of options; it is NP-hard for every even and every odd , while and remain open. Weighting each arc of the majority tournament by its margin reduces the problem to minimum-weight feedback arc set (FAS). The fewest voters inducing a tournament is its McGarvey number, and its predictability is the largest supermajority threshold at which is inducible. We refute three conjectures on inducibility. (i) In any tournament, every minimum FAS is a minimal hitting set of the directed 3-cycles, strengthening a theorem of Milosz, Hamel and Pierrot; both of their conjectures fail: the 3-cycle extension for all odd , and the equality at . (ii) The threshold conjecture proposed by Shepardson and Tovey fails for , exactly on the boundary (predictability ). (iii) For it fails strictly: the Paley tournament on 43 vertices, with predictability , is not the majority of any 5 voters, making it the first explicit tournament of modest size beyond the reach of five voters.
Cite
@article{arxiv.2607.26690,
title = {Tournaments determined by three and five voters},
author = {Leonid Chindelevitch and Ararat Harutyunyan},
journal= {arXiv preprint arXiv:2607.26690},
year = {2026}
}
Comments
29 pages, 7 figures