The congruence subgroup property for $Aut{F}_2$: A group-theoretic proof of Asada's theorem

Abstract

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 $Aut(F_2)$.

Final version

References in corpus (2)

• Developments on the congruence subgroup problem after the work of Bass, Milnor and Serre
• On the Index of Congruence Subgroups of Aut(F_n)

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