%0 Journal Article
%T The congruence subgroup property for $Aut F_2$: A group-theoretic proof of Asada's theorem
%A Kai-Uwe Bux
%A Mikhail Ershov
%A Andrei Rapinchuk
%J Mathematics
%D 2009
%I arXiv
%R 10.4171/GGD/130
%X The goal of this paper is to give a group-theoretic proof of the congruence subgroup property for $Aut(F_2)$, the group of automorphisms of a free group on two generators. This result was first proved by Asada using techniques from anabelian geometry, and our proof is, to a large extent, a translation of Asada's proof into group-theoretic language. This translation enables us to simplify many parts of Asada's original argument and prove a quantitative version of the congruence subgroup property for $Aut(F_2)$.
%U http://arxiv.org/abs/0909.0304v2