2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/153151Let $ϕ:G\rightarrow G$ be an endomorphism of a finitely generated residually finite group. R.~Hirshon asked if there exists~$n$ such that the restriction of $ϕ$ to $ϕ^n(G)$ is injective. We give an example to show that this is not always the case.DVI and Post-Script files onlyGroup Theorytext