Cohomological dimension and symmetric automorphisms of a free group.
Commensurations of Out
Let Out(Fn) denote the outer automorphism group of the free group Fn with n>3. We prove that for any finite index subgroup Γ<Out(Fn), the group Aut(Γ) is isomorphic to the normalizer of Γ in Out(Fn). We prove that Γ is co-Hopfian: every injective homomorphism Γ→Γ is surjective. Finally, we prove that the abstract commensurator Comm(Out(Fn)) is isomorphic to Out(Fn).
Conjugacy classes of series in positive characteristic and Witt vectors.
Let be the algebraic closure of and be the local field of formal power series with coefficients in . The aim of this paper is the description of the set of conjugacy classes of series of order for the composition law. This work is concerned with the formal power series with coefficients in a field of characteristic which are invertible and of finite order for the composition law. In order to investigate Oort’s conjecture, I give a description of conjugacy classes of series by means...
Construction of finite -groups with prescribed group of noncentral automorphisms
Contractibility of deformation spaces of -trees.