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arXiv · 2611.01148

Enumeration of plane hypermaps with a mixed boundary II

Thomas Lejeune
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Abstract

A plane hypermap with a boundary is a connected graph embedded in the plane with a distinguished face, and whose inner faces are properly face-bicolored. We say that such hypermaps are k-alternating if the colors of the faces adjacent to the distinguished face alternate at most 2k times when going counterclockwise. Eynard and Orantin, in [EO2005], have found a universal expression for the generating functions of k-alternating hypermaps as a surprisingly simple function of the generating function of 1-alternating hypermaps. In this article, we will provide combinatorial formulas for k-alternating hypermaps using specific subclasses of hypermaps in which each vertex can either be connected to a previously marked vertex, called accessible, or connected to all other vertices in what we call a blob. In particular, this method will allow us to derive the results from [EO2005] from a combinatorial perspective, and we anticipate that it will lead to the computation of asymptotics for hypermaps in future work. This article is naturally a sequel to, and most importantly a generalization of, the results in [BEL26], which deals essentially with the case of 1- and 2-alternating hypermaps.

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Thomas Lejeune. 2026-10-31. Enumeration of plane hypermaps with a mixed boundary II. https://arxiv.org/abs/2611.01148

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