Enumeration of planar two-face maps
نویسندگان
چکیده
We enumerate unrooted planar maps (up to orientation preserving homeomorphism) having two faces, according to the number of vertices and to their vertex and face degree distributions, both in the (vertex) labelled and unlabelled cases. We rst consider plane maps, i.e., maps which are embedded in the plane, and then deduce the case of planar (or sphere) maps, embedded on the sphere. A crucial step is the enumeration of two-face plane maps having an antipodal symmetry and use is made of Liskovets' method in the process. The motivation for this research comes from the topological classiication of Belyi functions. R esum e Nous d enombrons les cartes planaires ((a hom eomorphisme pr eservant l'orientation pr es) non point ees a deux faces, selon le nombre de sommets et selon la distribution des degr es des sommets et des faces, etiquet ees (aux sommets) ou non. Nous abordons d'abord les cartes planes, c'est-a-dire plong ees dans le plan, et d eduisons ensuite le cas des cartes planaires (ou sph eriques), plong ees sur la sph ere. Une etape cruciale est le d enombrement des cartes planes a deux faces admettant une sym etrie antipodale et la m ethode de Liskovets est utilis ee pour cela. La motivation de cette recherche provient de la classiication topologique des fonctions de Belyi.
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ورودعنوان ژورنال:
- Discrete Mathematics
دوره 222 شماره
صفحات -
تاریخ انتشار 2000