Abelian subgroups of the Torelli group.
Abhyankar's conjecture on Galois groups over curves.
About presentations of braid groups and their generalizations
In the paper we give a survey of rather new notions and results which generalize classical ones in the theory of braids. Among such notions are various inverse monoids of partial braids. We also observe presentations different from standard Artin presentation for generalizations of braids. Namely, we consider presentations with small number of generators, Sergiescu graph-presentations and Birman-Ko-Lee presentation. The work of V.~V.~Chaynikov on the word and conjugacy problems for the singular...
Actions and automorphisms of crossed modules
Actions de groupes sur les arbres
Actions of discrete groups on nonpositively curved spaces.
Actions of finite groups on C*-algebras.
Actions of finitely generated groups on -trees
We study actions of finitely generated groups on -trees under some stability hypotheses. We prove that either the group splits over some controlled subgroup (fixing an arc in particular), or the action can be obtained by gluing together actions of simple types: actions on simplicial trees, actions on lines, and actions coming from measured foliations on -orbifolds. This extends results by Sela and Rips-Sela. However, their results are misstated, and we give a counterexample to their statements.The...
Active sums I.
Given a generating family F of subgroups of a group G closed under conjugation and with partial order compatible with inclusion, a new group S can be constructed, taking into account the multiplication in the subgroups and their mutual actions given by conjugation. The group S is called the active sum of F, has G as a homomorph and is such that S/Z(S) ≅ G/Z(G) where Z denotes the center.The basic question we investigate in this paper is: when is the active sum S of the family F isomorphic to the...
Addendum and corrigendum to «Automorfismi che fissano i centralizzanti di un gruppo»
Adjoint groups and the Mal'cev correspondence (a tale of four functors)
Affine braid group actions on derived categories of Springer resolutions
In this paper we construct and study an action of the affine braid group associated with a semi-simple algebraic group on derived categories of coherent sheaves on various varieties related to the Springer resolution of the nilpotent cone. In particular, we describe explicitly the action of the Artin braid group. This action is a “categorical version” of Kazhdan-Lusztig-Ginzburg’s construction of the affine Hecke algebra, and is used in particular by the first author and I. Mirković in the course...
Affine completeness of complete lattice ordered groups
Affine permutations and inversion multigraphs.
Affine permutations of type .
Affine Weyl groups as infinite permutations.
Alcune proprietà gruppali invarianti per semi-isomorfismi
Algebraic groups with a distinguished conjugacy class.
Algebraic properties of mapping class groups of surfaces
Algebraic sets and coordinate groups for a free nilpotent group of nilpotency class 2.