Mapping tori of free group automorphisms are coherent


The mapping torus of an endomorphism $\Phi$ of a group $G$ is the HNN-extension $G_{*G}$ with bonding maps the identity and $\Phi$. We show that a mapping torus of an injective free group endomorphism has the property that its finitely generated subgroups are finitely presented and, moreover, these subgroups are of finite type.


Mark Feighn

Michael Handel