On subsemigroup lattices of aperiodic groups.
On tame automorphisms of some metabelian groups.
On the Boffa alternative
Let G* denote a nonprincipal ultrapower of a group G. In 1986 M.~Boffa posed a question equivalent to the following one: if G does not satisfy a positive law, does G* contain a free nonabelian subsemigroup? We give the affirmative answer to this question in the large class of groups containing all residually finite and all soluble groups, in fact, all groups considered in traditional textbooks on group theory.
On the Burnside problem for groups of even exponent.
On the Cantor-Bendixson rank of metabelian groups
We study the Cantor-Bendixson rank of metabelian and virtually metabelian groups in the space of marked groups, and in particular, we exhibit a sequence of 2-generated, finitely presented, virtually metabelian groups of Cantor-Bendixson rank .
On the centralizer of an automorphism of order 2 of the Burnside group .
On the character variety of group representations in SL (2, C) and PSL (2, C).
On the closed left ideals of the group algebra
On the combinatorics of permutations. (Zur Kombinatorik von Permutationen.)
On the Conjugacy Problem in a Free Product with Commuting Subgroups.
On the conjugate type vector and the structure of a normal subgroup
Let be a normal subgroup of a group . The structure of is given when the -conjugacy class sizes of is a set of a special kind. In fact, we give the structure of a normal subgroup under the assumption that the set of -conjugacy class sizes of is , where , and are distinct primes for , .
On the cyclic subgroup separability of free products of two groups with amalgamated subgroup.
On the diameter of the intersection graph of a finite simple group
Let be a finite group. The intersection graph of is an undirected graph without loops and multiple edges defined as follows: the vertex set is the set of all proper nontrivial subgroups of , and two distinct vertices and are adjacent if , where denotes the trivial subgroup of order . A question was posed by Shen (2010) whether the diameters of intersection graphs of finite non-abelian simple groups have an upper bound. We answer the question and show that the diameters of intersection...
On the dynamics and the fixed subgroup of a free group automorphism.
On the Embedding of Semigroups into Nilpotent Groups
On the existence of -local subgroups in a group.
On the existence of group localizations under large-cardinal axioms.
Uno de los problemas abiertos más antiguos de la teoría de grupos categórica es si todo par ortogonal (formado por una clase de grupos y una clase de homomorfismos que se determinan mutuamente por ortogonalidad en el sentido de Freyd-Kelly), se halla asociado a un funtor de localización. Se sabe que esto es cierto si se acepta la validez de un cierto axioma de cardinales grandes (el principio de Vopenka), pero no se conoce ninguna demostración mediante los axiomas ordinarios (ZFC) de la teoría de...
On the existence of universal covering spaces for metric spaces and subsets of the Euclidean plane
We prove several results concerning the existence of universal covering spaces for separable metric spaces. To begin, we define several homotopy-theoretic conditions which we then prove are equivalent to the existence of a universal covering space. We use these equivalences to prove that every connected, locally path connected separable metric space whose fundamental group is a free group admits a universal covering space. As an application of these results, we prove the main result of this article,...
On the existence of universal rational structures for groups.
On the exponent of the product of two groups