Our main contribution is a surprising polynomial-time algorithm for weighed coalitional manipulation of four-candidate Copeland (also known as Llull) elections. On the technical side, our algorithm relies on a polynomial-time routine that solves a variant of the partition problem. We also show that there is a pseudo-polynomial-time algorithm for weighted coalitional manipulation with a fixed number of candidates under any anonymous rule with a polynomial-time winner-determination procedure.
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