Contingent vote
The contingent vote is the ranked version of top-two runoff. Like in instant-runoff voting, candidates are eliminated based on their first preferences, but the contingent vote only has two rounds. In the first round, everybody but the top two is eliminated, then the finalist who beats the other pairwise wins.
Like instant-runoff voting, the contingent vote fails monotonicity and passes later-no-harm and later-no-help. Unlike IRV, it is summable.
See Contingent vote on Wikipedia for more information.
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