Séminaire Lotharingien de Combinatoire, B70e (2014), 28 pp.

Robert Cori and Gábor Hetyei

Counting Genus One Partitions and Permutations

Abstract. We prove the conjecture by M. Yip stating that counting genus one partitions by the number of their elements and parts yields, up to a shift of indices, the same array of numbers as counting genus one rooted hypermonopoles. Our proof involves representing each genus one permutation by a four-colored noncrossing partition. This representation may be selected in a unique way for permutations containing no trivial cycles. The conclusion follows from a general generating function formula that holds for any class of permutations that is closed under the removal and reinsertion of trivial cycles. Our method also provides a new way to count rooted hypermonopoles of genus one, and puts the spotlight on a class of genus one permutations that is invariant under an obvious extension of the Kreweras duality map to genus one permutations.

Received: July 21, 2013. Accepted: December 27, 2013. Final Version: January 10, 2014.

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