Ranked pairs

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Ranked Pairs (RP), also known as the Tideman method, is a tournament-style system of ranked voting first proposed by Nicolaus Tideman in 1987.

If there is a candidate who is preferred over the other candidates, when compared in turn with each of the others, the ranked-pairs procedure guarantees that candidate will win. Therefore, the ranked-pairs procedure complies with the Condorcet winner criterion—that is, it is a Condorcet method.

Ranked pairs begins with a round-robin tournament, where the one-on-one margins of victory for each possible pair of candidates are compared to find a majority-preferred candidate; if such a candidate exists, they are immediately elected. Otherwise, if there is a Condorcet cycle (a rock-paper-scissors-like sequence A > B > C > A) of three or more candidates then the cycle is broken by dropping the "weakest" election in the cycle, i.e. the one that is closest to being tied.