The concept of the Condorcet winner has become central to most electoral models in the political economy literature. A Condorcet winner is the alternative preferred by a plurality in every pairwise competition; the notion of a k-winner generalizes that of a Condorcet winner. The k-winner is the...

An extension rule assigns to each fractional tournament x (specifying, for every pair of social alternatives a and b, the proportion xab of voters who prefer a to b) a random choice function y (specifying a collective choice probability distribution for each subset of alternatives), which...