On Finite Index Subgroups of a Universal Group
نویسنده
چکیده
The orbifold group of the Borromean rings with singular angle 90 degrees, U , is a universal group, because every closed oriented 3–manifold M3 occurs as a quotient space M3 = H3/G, where G is a finite index subgroup of U . Therefore, an interesting, but quite difficult problem, is to classify the finite index subgroups of the universal group U . One of the purposes of this paper is to begin this classification. In particular we analyze the classification of the finite index subgroups of U that are generated by rotations.
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تاریخ انتشار 2008