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We give several sufficient conditions for a double of a free group along a cyclic subgroup to contain a surface subgroup.

We prove that the set of limit groups is recursively enumerable, answering a question of Delzant. One ingredient of the proof is the observation that a finitely presented group with local retractions (à la Long and Reid) is coherent and, furthermore, there exists an algorithm that computes presentations for finitely generated subgroups. The other main… (More)

- Emily Hamilton, Henry Wilton, Pavel Zalesskii
- J. London Math. Society
- 2013

- Henry Wilton
- 2008

A celebrated theorem of Marshall Hall Jr. implies that finitely generated free groups are subgroup separable and that all of their finitely generated subgroups are retracts of finite-index subgroups. We use topological techniques inspired by the work of Stallings to prove that all limit groups share these two properties. This answers a question of Sela.… (More)

- Henry Wilton
- 2008

We use wreath products to provide criteria for a group to be conjugacy separable or omnipotent. These criteria are in terms of virtual retractions onto cyclic subgroups. We give two applications: a straightforward topological proof of the theorem of Stebe that infiniteorder elements of Fuchsian groups (of the first type) are conjugacy distinguished, and a… (More)

- Henry Wilton
- 2008

Elementarily free groups are the finitely generated groups with the same elementary theory as free groups. We prove that elementarily free groups are subgroup separable, answering a question of Zlil Sela. Limit groups arise naturally in the study of the set of homomorphisms to free groups and, in the guise of fully residually free groups, have long been… (More)

- Henry Wilton
- 2008

A celebrated theorem of Marshall Hall implies that finitely generated free groups are subgroup separable and that all of their finitely generated subgroups are retracts of finite-index subgroups. We use topological techniques inspired by the work of Stallings to prove that all limit groups share these two properties. This answers a question of Sela and… (More)

- OWEN COTTON - BARRATT, Henry Wilton
- 2009

We use the theory of group actions on profinite trees to prove that the fundamental group of a finite, 1-acylindrical graph of free groups with finitely generated edge groups is conjugacy separable. This has several applications: we prove that positive, C(1/6) one-relator groups are conjugacy separable; we provide a conjugacy separable version of the Rips… (More)

- Henry Wilton
- 2009

We classify those closed 3-manifolds whose fundamental groups are residually free. To be precise, let M be any compact, prime 3manifold with (possibly empty) incompressible, toral boundary and suppose that the fundamental group of M is non-trivial and residually free. Then M ∼= Σ × S1, where Σ is a surface with residually free fundamental group. We also… (More)

- Henry Wilton
- 2008

A celebrated theorem of Marshall Hall implies that finitely generated free groups are subgroup separable and that all of their finitely generated subgroups are retracts of finite-index subgroups. We use topological techniques inspired by the work of Stallings to prove that all limit groups share these two properties. This answers a question of Sela and… (More)