Counting non-equivalent coverings and non-isomorphic maps for Riemann surfaces
نویسنده
چکیده
The main result of the paper is a new formula for the number of conjugacy classes of subgroups of a given index in a finitely generated group. As application of this result a simple proof of the formula for the number of non-equivalent coverings over surface (orientable or not, bordered or not) is given. Another application is a formula for the number of non-isomorphic unrooted maps on an orientable closed surface with a given number of edges.
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تاریخ انتشار 2005