Mapping Tori of Free Group Automorphisms are Coherent

Abstract

The mapping torus of an endomorphism Φ of a group G is the HNNextension G * G with bonding maps the identity and Φ.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.