# Very Hard Electoral Control Problems

Zack Fitzsimmons,
Edith Hemaspaandra,
Alex Hoover,
David E. Narváez

October 2019

### Abstract

It is important to understand how the outcome of an election can be modified by an agent with control over the structure of the election. Electoral control has been studied for many election systems, but for all studied systems the winner problem is in P, and so control is in NP. There are election systems, such as Kemeny, that have many desirable properties, but whose winner problems are not in NP. Thus for such systems control is not in NP, and in fact we show that it is typically complete for Σp2 (i.e., NPNP, the second level of the polynomial hierarchy). This is a very high level of complexity. Approaches that perform quite well for solving NP problems do not necessarily work for Σp2-complete problems. However, answer set programming is suited to express problems in Σp2, and we present an encoding for Kemeny control.

Publication

In *Association for the Advancement of Artificial Intelligence 2019*

###### Cryptography PhD Student

A regular guy with broad interests across cyrptography, computer security, quantum computing, and more.