Talk:IRV Prime

Hello, Condorcet and Later-no-harm are incompatible - see proof in Woodall. Could you run your method through the example provided there and update the article? Kristomun (talk) 09:12, 31 July 2021 (UTC)

So if you look at Woodall's full paper, he does not say they're incompatible:

 In general, CONDORCET is incompatible with LATER-NO-HELP, LATER-NO-HARM,
 MONO-RAISE-DELETE, MONO-SUB-PLUMP and, in the presence of PLURALITY, MONO-ADD-TOP. 

"in general" --Marcosb (talk) 22:39, 3 August 2021 (UTC)

Arrow/IIA

As I understand it, the reference to satisfying Arrow's theorem is meant to imply that the method satisfies IIA. But I don't think that's possible.

In a Condorcet cycle like this:

35: A>B>C
30: B>C>A
25: C>A>B

Who wins in IRV Prime? If it's A, then eliminating B (irrelevant candidate) should make C win by majority rule. If it's B, then eliminating C makes A win; and if it's C, then eliminating A makes B win. I may be missing something, though! :-) Kristomun (talk) 22:22, 31 July 2021 (UTC)

Running through the IRV-Prime steps, first we do classic IRV, which eliminates C & finds winners={A}: A: 60 B: 30

We now see if any candidate can win against A (we know B can't), i.e. WinnersPrime={C}: C: 55 A: 35

And as such C is the winner in IRV-Prime; this is a classic case of A=Rock, B=Scissors, C=Paper; if I phrase it to you as "suppose B & C voters were to go up against A: which candidate should they stand behind?"

--Marcosb (talk) 22:39, 3 August 2021 (UTC)