Usually a voting rule requires agents to give their preferences as linear orders. However, in some cases it is impractical for an agent to give a linear order over all the alternatives. It has been suggested to let agents submit partial orders instead. Then, given a voting rule, a profile of partial orders, and an alternative (candidate) c, two important questions arise: first, is it still possible for c to win, and second, is c guaranteed to win? These are the possible winner and necessary winner problems, respectively. Each of these two problems is further divided into two sub-problems: determining whether c is a unique winner (that is, c is the only winner), or determining whether c is a co-winner (that is, c is in the set of winners). We consider the setting where the number of alternatives is unbounded and the votes are unweighted. We completely characterize the complexity of possible/necessary winner problems for the following common voting rules: a class of positional scoring rules (including Borda), Copeland, maximin, Bucklin, ranked pairs, voting trees, and plurality with runoff.
UNSW（新南威尔士大学）；NICTA（澳大利亚国家信息与通信技术研究院）；University of Rostock（罗斯托克大学）
Schulze的规则被用于包括Wikimedia和Debian在内的大量组织的选举中。其流行的部分原因是大量的公理性质，如单调性和孔多塞一致性，它满足。我们确定了一个潜在的缺点舒尔茨的规则：它是计算容易受到操纵。特别是，我们证明了计算未加权联盟操纵（UCM）是多项式的任何数量的机械手。这一结果适用于UCM的唯一获胜者和共同获胜者版本。这解决了Parkes and Xia（2012）提出的一个未决问题。我们还证明了计算一个加权联盟操纵（WCM）是多项式的有限数量的候选人。最后，我们讨论了唯一赢家UCM问题和共同赢家UCM问题之间的关系，并认为他们有实质上不同的充分必要条件存在一个成功的操纵。
Navigating the Complexity Landscape of Nominee Selection in Schulze Voting
P.J. Šafárik University（P.J.沙法里克大学）；Heinrich-Heine-Universität Düsseldorf（杜塞尔多夫海因里希·海涅大学）；AGH University of Krakow（克拉科夫AGH科技大学）；Czech Technical University in Prague（捷克布拉格理工大学）；ELTE Centre for Economic and Regional Studies（布达佩斯罗兰大学经济与区域研究中心）；Budapest University of Technology and Economics（布达佩斯技术与经济大学）
On the Complexity of Winner Determination and Strategic Control in Conditional Approval Voting
Athens University of Economics and Business（雅典经济与商业大学）；Archimedes, Athena Research Center（阿基米德、雅典研究中心）；Input Output Global (IOG)（输入输出全球（IOG））；University of Warsaw（华沙大学）
