Automorphisms of the Baumslag-Gersten group
Abstract
We classify homomorphisms of the Baumslag-Gersten group into itself. We prove it is Hopfian and co-Hopfian. We show that the group of outer automorphisms of the Baumslag-Gersten group is isomorphic to the dyadic rationals with the addition operation. These results are not new. They were obtained by Andrew M. Brunner in Brunner. However, our exposition is self-contained and, hopefully, more accessible for some readers.
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