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arXiv · 2604.05728

An improved characterisation of inner automorphisms of groups

Francesco Fournier-Facio
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Abstract

We show that every group $G$ embeds malnormally into a simple, complete co-Hopfian group $H$. This implies that a non-trivial endomorphism of $G$ extends to $H$ if and only if it is an inner automorphism, strengthening a theorem of Schupp and answering a question of Bergman.

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Francesco Fournier-Facio. 2026-04-07. An improved characterisation of inner automorphisms of groups. https://arxiv.org/abs/2604.05728

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