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We prove the following results: (1) Every group is a maximal subgroup of some free idempotent generated semigroup. (2) Every finitely presented group is a maximal subgroup of some free idempotent generated semigroup arising from a finite…

Group Theory · Mathematics 2011-08-02 Robert Gray , Nik Ruskuc

A continuous family of non-outer conjugate aperiodic automorphisms whose crossed-products are all isomorphic is given on every interpolated free group factor. An explicit "duality" relationship between compact co-commutative Kac algebra…

Operator Algebras · Mathematics 2019-05-21 Fumio Hiai , Yoshimichi Ueda

We prove a analog of Kurosh theorem for countable Borel equivalence relations giving the structure of sub-relations in free products.

Dynamical Systems · Mathematics 2009-02-24 Aurelien Alvarez

We show that the freeness problems for automaton semigroups and for automaton monoids are undecidable and, thereby, solve an open problem listed by Grigorchuk, Nekrashevych and Sush\-chansk\u{\i}i. We achieve this using a new technique to…

Formal Languages and Automata Theory · Computer Science 2025-02-19 Daniele D'Angeli , Emanuele Rodaro , Jan Philipp Wächter

We prove that the finitely presentable subgroups of residually free groups are separable and that the subgroups of type $\mathrm{FP}_\infty$ are virtual retracts. We describe a uniform solution to the membership problem for finitely…

Group Theory · Mathematics 2007-06-29 Martin R. Bridson , Henry Wilton

We consider the class of groups whose word problem is poly-context-free; that is, an intersection of finitely many context-free languages. We show that any group which is virtually a finitely generated subgroup of a direct product of free…

Group Theory · Mathematics 2015-10-09 Tara Brough

This paper is devoted to the investigation of the property of order separability for HNN extensions and free products with commutative subgroups. Particularly it was proven that HNN extension of a free group with maximal connected cyclic…

Group Theory · Mathematics 2010-07-21 Vladimir V. Yedynak

In this paper we first state the classification of the prolongations of complex free fundamental graded Lie algebras. Next we introduce the notion of free pseudo-product fundamental graded Lie algebras and study the prolongations of complex…

Differential Geometry · Mathematics 2012-06-28 Tomoaki Yatsui

Free products of two residually finite groups with amalgamated retracts are considered. It is proved that a cyclic subgroup of such a group is not finitely separable if, and only if, it is conjugated with a subgroup of a free factor which…

Group Theory · Mathematics 2013-08-19 P. A. Bobrovskii , E. V. Sokolov

In this paper, we observe the amalgamated free product structure of a Graph W*-probability space. In [16] and [17], we already observed the operator-valued freeness conditions on a graph W*-algebra. By using the conditions, we will consider…

Operator Algebras · Mathematics 2007-05-23 Ilwoo Cho

We prove that the cup product of $\Delta$-decomposable quasimorphisms, Brooks quasimorphisms or Rolli quasimorphisms with any bounded cohomology class of arbitrary positive degree is trivial.

Group Theory · Mathematics 2022-03-29 Sofia Amontova , Michelle Bucher

We introduce a noncommutative binary operation on matroids, called free product. We show that this operation respects matroid duality, and has the property that, given only the cardinalities, an ordered pair of matroids may be recovered, up…

Combinatorics · Mathematics 2007-05-23 Henry Crapo , William Schmitt

We prove that a subquandle of a free quandle is free.

Group Theory · Mathematics 2019-04-16 Sergei O. Ivanov , Georgii Kadantsev , Kirill Kuznetsov

We describe an algorithm for deciding whether or not a given finitely generated torsion-free nilpotent group is decomposable as the direct product of nontrivial subgroups.

Group Theory · Mathematics 2015-12-18 Gilbert Baumslag , Charles F. Miller , Gretchen Ostheimer

An approach to identify the normal subgroups determined by ideals in free group rings with the help of the derived functors of non-additive functors is explored. A similar approach, i.e., via derived functors, for computing limits of…

Group Theory · Mathematics 2016-05-27 Roman Mikhailov , Inder Bir S. Passi

We consider the hidden subgroup problem on the semi-direct product of cyclic groups $\Z_{N}\rtimes\Z_{p}$ with some restriction on $N$ and $p$. By using the homomorphic properties, we present a class of semi-direct product groups in which…

Quantum Physics · Physics 2009-09-30 Dong Pyo Chi , Jeong San Kim , Soojoon Lee

The isomorphism problem for [free abelian]-by-free groups is unsolvable.

Group Theory · Mathematics 2008-12-15 Gilbert Levitt

We give an explicit description of the free objects in the quasivariety of adequate semigroups, as sets of labelled directed trees under a natural combinatorial multiplication. The morphisms of the free adequate semigroup onto the free…

Rings and Algebras · Mathematics 2009-05-08 Mark Kambites

We establish explicit expressions for the $K$-theory classes of higher Kazhdan projections for amalgamated product groups $\mathbb{Z}_m*_{\mathbb{Z}_d}\mathbb{Z}_n$. Our approach follows the methodology developed by Pooya and Wang for free…

Operator Algebras · Mathematics 2025-07-09 Baiying Ren

A finitely generated group is lacunary hyperbolic if one of its asymptotic cones is an $\mathbb{R}$-tree. In this article we give a necessary and sufficient condition on lacunary hyperbolic groups in order to be stable under free product by…

Group Theory · Mathematics 2020-02-21 Krishnendu Khan