[EM] "Beatpath GMC" compliance a mistaken standard?

Paul Kislanko kislanko at airmail.net
Sun Jan 11 00:27:58 PST 2009

Arrrgggg. Explain, someone, anyone, how MM can change an (A B) to an (A B C)
possible winner set by adding voters for A. 

-----Original Message-----
From: election-methods-bounces at lists.electorama.com
[mailto:election-methods-bounces at lists.electorama.com] On Behalf Of
Kristofer Munsterhjelm
Sent: Sunday, January 11, 2009 2:23 AM
To: election-methods at electorama.com
Cc: 'Markus Schulze'
Subject: Re: [EM] "Beatpath GMC" compliance a mistaken standard?

Paul Kislanko wrote:
> This still makes no sense to me, since C has no more a majority in case 2
> than it had in case 1.
> If mutual majority selects (A B) in case 1 and (A B C) in case 2, it makes
> no sense at all and should never be mentioned again. 

Mutual majority can still be useful. Let's make an analogy to Condorcet. 
The Condorcet criterion elects the CW if there is one. In other words, 
if there is a CW and that CW is candidate X, then the set from which 
Condorcet methods elect is { X }. If there is no CW, and the candidates 
for election are {A B C ... X }, then the set from which Condorcet 
methods elect is {A B C ... X }.

Thus, Condorcet is useful when there is indeed a CW, but does nothing 
when there isn't.

So it is with mutual majority as well. When there's a set that a 
majority ranks above all the others, then a method that passes mutual 
majority must elect from that set. When there is no such set, the method 
is free to pick any candidate yet still pass mutual majority.

In that light, mutual majority seems very reasonable indeed: if there is 
a set so that a majority prefers that set to all others outside the set, 
then a candidate within that set should be elected. It's simply 
"majority" transported to sets.

(And on another note, sorry for not mailing you this directly as well, 
Paul, but airmail.net seems to think my ISP is a dirty spammer.)
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