[EM] Cabal equilibria in voting

[Peter de Blanc]

When I posted about cabal equilibria in January, Jameson Quinn asked me 
when honest voting is a cabal equilibrium. I thought about that question 
recently, and for Condorcet methods I have a partial answer.

If there exists a double Condorcet winner, then an honest vote is a 
cabal equilibrium.

A double Condorcet winner is a candidate who is preferred over every 
other pair of candidates by a majority. That is, if C is the winner, 
then for any other pair of candidates {A, B}, the set of voters who 
ranked C above both A and B comprises a majority of the electorate.

The proof is posted to my blog here: http://www.spaceandgames.com/?p=134

  - Peter de Blanc