the No Spoiling criterion

[Lowell Bruce Anderson]

    If candidate X would be elected when Y is not a candidate, 
    then X or Y will be elected if Y is a candidate (assuming 
    the voters don't alter their relative orderings of the 
    non-Y candidates).

Basically, this is what Arrow's theorem says is impossible for a 
rank-order voting method to satisfy (without a "dictator" or other 
such contrivance).

Bruce