[EM] PR pairwise

[Forest Simmons]

Here's a crude PR pairwise, sequential method:

When comparing two candidates C1 and C2 on a ballot that ranks C1 ahead of
C2, give the ballot a weight of the reciprocal of one more than the number
of candidates ranked above C1 (on this ballot) who have already been
elected.

Two winner example:

66 A>B>C
34 C>B>A

Candidate A gets elected in the first round.

In the second round all of the ballots from the first faction get half
weight, so C beats B, 34 to 33.

If two voters defected from the minority faction, A and B would be the
winners.

This method can be refined in various ways that I won't go into now, and
adapted to Dyadic and Universal Approval as well.

Forest