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Mapping tori of free group automorphisms are coherent

Mark Feighn, Michael Handel

math.GRarXiv:math/9905209

Abstract

The mapping torus of an endomorphism Φof a group G is the HNN-extension 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.

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