Kevin--
You proposed the following criterion:
"If a majority of all the voters vote A in first or equal first, and B in last or equal last, then B mustn't win."
I reply:
In IRV or ERIRV, if a majority rank A in 1st place, and B in last place, then B isn't a contender for the win. A has a vote total more than half the number of voters. The winner will the the majority-vote-total candidate who has the most votes. That might be A, or some other such candidate, but it won't be B, since B is ranked last by a majority. B can't win.
IRV and ERIRV pass your criterion.
The fact that Plurality and IRV pass your criterion and fail WDSC makes it odd that you say that your criterion implies WDSC, if by that you mean that compliance with your criterion implies compliance with WDSC.
Mike Ossipoff
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