[EM] Ultimate SPE Agenda Processing: Sink Swap Bubble

[Kristofer Munsterhjelm]

On 11.04.2023 19:55, Forest Simmons wrote:
> Suppose someone provides a list of candidates already sorted pairwise.
> 
> Now do Benham elimination ... start at the loser end of the list and 
> eliminate candidates one by one until there is (according to a fresh set 
> of ballots) a CW among the uneliminated.
> 
> How much incentive if any to rank insincerely?

Since Condorcet is incompatible with LNH, there will be some incentive 
to either truncate or random-fill (depending on the situation). I would 
also imagine that if the strategists know the list ahead of time, and 
they know that it's A>B>C>D, then if C is the CW, A is their favorite, 
and A beats B pairwise, they'll have an incentive to engineer a false 
cycle by burying C under B.

If they don't know the list, it's much harder to do. It reminds me of 
the Conitzer and Sandholm preround, which makes strategy harder to 
devise in practice, and just how hard depends on what information the 
strategists have (see 
https://www.cs.cmu.edu/~sandholm/voting_tweaks.ijcai03.pdf). (In 
practice, this doesn't matter, because most elections have relatively 
few candidates; it's just the "it depends on information" aspect that's 
similar.)

-km