Texas A&M University, Department of
Mathematics, 216 Milner Hall, 31st of January 2007, 3:00-3:50
Groups and Dynamics Seminar
Profinite surface
groups
Pavel Zalesskiĭ of Universidade de
Brasília, Brazil
We discuss the subgroup structure of profinite surface groups, which
are defined as profinite completions of the fundamental groups of
compact Riemann surfaces. In particular, a description of normal
(subnormal, accessible) subgroups will be presented. After this we show
how these results are used to give a complete solution of the
congruence subgroup problem for arithmetic subgroups in SL_2(R).