[EM] Some easier burial resistance criteria

[Kristofer Munsterhjelm]

I find it kind of hard to reason about burial-resistant Condorcet
methods because DMTBR is such a difficult criterion to pass. Perhaps the
following criteria will be good steps on the way:

Mutual majority burial resistance (MMBR): If A is in the smallest mutual
majority set and wins, then voters who prefer B to A can't make B win by
burying A under a candidate X not in the smallest mutual majority set.

Pareto-dominated BR: If A wins and X is a Pareto-dominated candidate,
then voters who prefer B to A can't make B win by burying A under X.

DMTBR seems to rely on that there can't be more than two disjoint solid
coalitions of the same cardinality supported by more than a third of the
voters. Similarly, MMBR would have to rely on there being only one
smallest mutual majority set. I may have an idea for a method that
passes MMBR, but I would have to check that my reasoning is correct.

But as for Pareto-dominated BR, I don't yet have a clue.

-km