[EM] Strategy-free criterion

[Kevin Venzke]

Hi all,

When I test for SFC compliance the rule on cast votes is that if there is no
majority over A, and A has a majority over B, then B can't win.

This is kind of a flip side of MD / SDSC because, if you were forced to explain MD
in terms of a graph of majority-strength defeats, it would say that if A has a
majority over B and B doesn't have a majority over anyone, then B can't win.

MD basically says that if there are two frontrunners and everyone truncates their
less liked frontrunner, then the worse frontrunner won't win. If this property
doesn't hold, it means the majority has done something to stop the method from
"seeing" their majority, which is surely that they ranked other candidates above
the preferred frontrunner. So MD is mostly about compromise incentive.

SFC is probably going to be about truncation. When a method fails it, most likely
it's because the majority gave the election away to a less liked compromise choice.
For example:

20 C>A>B
35 A>B
5 B
40 D

Here B is the implicit approval winner, but by SFC B should not win, because it
means it was not safe for the A voters to rank B.

I would not like to see SFC as totally obsolete, since it was one of the motivating
criteria (along with MD and weak FBC) for my methods MDDA and MAMPO :)

Kevin
votingmethods.net