[EM] Approval, but not IRV, always has unreversed Nash equilibria

[MIKE OSSIPOFF]

As we on EM have been using the term for voting systems, a Nash equilibrium 
is an outcome, and the votes configuration that caused it, that no set of 
voters can improve on for themselves by voting differently.

With IRV there will often by situations (configurations of candidates, and 
voters' preferences among candidates) in which the only Nash equilibria are 
ones in which some voters reverse a preference in order to save the win of a 
CW.

With Approval every situation has at least one Nash equilibrium in which no 
one reverses a sincere preference.

By the way, what I said about IRV above is also true of Plurality, Runoff, 
Borda, and margins Condorcet.

Mike Ossipoff

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