306 citations
Counting papers with at most 25 authors, so collaboration author lists do not stand in for the people here.
- Universidade do PortoPT174 papers
- University of CoimbraPT98 papers
- University of MinhoPT81 papers
- University of LisbonPT24 papers
- Centre National de la Recherche ScientifiqueFR22 papers
- Instituto Superior TécnicoPT22 papers
- UCLouvainBE13 papers
- Universidade Federal da BahiaBR13 papers
- Centro de Análise Matemática Geometria e Sistemas DinâmicosPT10 papers
- Pontifícia Universidade Católica do Rio de JaneiroBR10 papers
- Universidad de La LagunaES9 papers
- Universidade Federal do Rio de JaneiroBR9 papers
46 papers · 1 filter
Holonomy theorem for finite semigroups
John Rhodes, Anne Schilling, Pedro V. Silva
We provide a simple proof of the Holonomy Theorem using a new Lyndon-Chiswell length function on the Karnofsky-Rhodes expansion of a semigroup. Unexpectedly, we have both a left an…
Locally countable pseudovarieties
Jorge Almeida, Ondrej Klíma
The purpose of this paper is to contribute to the theory of profinite semigroups by considering the special class consisting of those all of whose finitely generated closed subsemi…
Recognizing pro-R closures of regular languages
Jorge Almeida, José Carlos Costa, Marc Zeitoun
Given a regular language L, we effectively construct a unary semigroup that recognizes the topological closure of L in the free unary semigroup relative to the variety of unary sem…
On the lattice of subgroups of a free group: complements and rank
Jordi Delgado, Pedro V. Silva
A -complement of a subgroup is a subgroup such that . If we also ask to have trivial inters…
On the group of a rational maximal bifix code
Jorge Almeida, Alfredo Costa, Revekka Kyriakoglou +1
We give necessary and sufficient conditions for the group of a rational maximal bifix code to be isomorphic with the -group of , when is recurrent and …
Pseudovarieties of ordered completely regular semigroups
Jorge Almeida, Ondřej Klíma
This paper is a contribution to the theory of finite semigroups and their classification in pseudovarieties, which is motivated by its connections with computer science. The questi…
Generating maximal subgroups of finite almost simple groups
Andrea Lucchini, Claude Marion, Gareth Tracey
For a finite group , let denote the minimal number of elements required to generate . In this paper, given a finite almost simple group and any maximal subgroup $H…
On the insertion of n-powers
J. Almeida, O. Klíma
In algebraic terms, the insertion of -powers in words may be modelled at the language level by considering the pseudovariety of ordered monoids defined by the inequality $1\le x…
Nilpotency and strong nilpotency for finite semigroups
J. Almeida, M. Kufleitner, M. H. Shahzamanian
Nilpotent semigroups in the sense of Mal'cev are defined by semigroup identities. Finite nilpotent semigroups constitute a pseudovariety, , which has finite rank. The…
A note on the finite basis and finite rank properties for pseudovarieties of semigroups
J. Almeida, M. H. Shahzamanian
The finite basis property is often connected with the finite rank property, which it entails. Many examples have been produced of finite rank varieties which are not finitely based…
Reducibility versus definability for pseudovarieties of semigroups
J. Almeida, O. Klíma
It is easy to show that a pseudovariety which is reducible with respect to an implicit signature for the equation can also be defined by -identities. We present severa…
The semaphore codes attached to a Turing machine via resets and their various limits
John Rhodes, Anne Schilling, Pedro V. Silva
We introduce semaphore codes associated to a Turing machine via resets. Semaphore codes provide an approximation theory for resets. In this paper we generalize the set-up of our pr…
The omega-inequality problem for concatenation hierarchies of star-free languages
J. Almeida, O. Klíma, M. Kunc
The problem considered in this paper is whether an inequality of omega-terms is valid in a given level of a concatenation hierarchy of star-free languages. The main result shows th…
Complete kappa-reducibility of pseudovarieties of the form DRH
Jorge Almeida, Célia Borlido
We denote by kappa the implicit signature that contains the multiplication and the (omega-1)-power. It is proved that for any completely kappa-reducible pseudovariety of groups H,…
Some reducibility properties for pseudovarieties of the form DRH
Célia Borlido
Let H be a pseudovariety of groups and DRH be the pseudovariety containing all finite semigroups whose regular R-classes belong to H. We study the relationship between reducibility…
The rank of variants of nilpotent pseudovarieties
J. Almeida, M. H. Shahzamanian
We investigate the rank of pseudovarieties defined by several of the variants of nilpotency conditions for semigroups in the sense of Mal'cev. For several of them, we provide finit…
The pro-nilpotent group topology on a free group
J. Almeida, M. H. Shahzamanian, B. Steinberg
In this paper, we work on the pro-nilpotent group topology of a free group. First we investigate the closure of the product of finitely many subgroups of a free group in the pro-ni…
Representations of relatively free profinite semigroups, irreducibility, and order primitivity
J. Almeida, O. Klíma
We establish that, under certain closure assumptions on a pseudovariety of semigroups, the corresponding relatively free profinite semigroups freely generated by a non-singleton fi…
Pointlike reducibility of pseudovarieties of the form
J. C. Costa, C. Nogueira, M. L. Teixeira
In this paper, we investigate the reducibility property of semidirect products of the form relatively to (pointlike) systems of equations of the form …
Random walks on semaphore codes and delay de Bruijn semigroups
John Rhodes, Anne Schilling, Pedro V. Silva
We develop a new approach to random walks on de Bruijn graphs over the alphabet through right congruences on , defined using the natural right action of . A major rol…
A geometric interpretation of the Schützenberger group of a minimal subshift
J. Almeida, A. Costa
The first author has associated in a natural way a profinite group to each irreducible subshift. The group in question was initially obtained as a maximal subgroup of a free profin…
Reducibility of pointlike problems
J. Almeida, J. C. Costa, M. Zeitoun
We show that the pointlike and the idempotent pointlike problems are reducible with respect to natural signatures in the following cases: the pseudovariety of all finite semigroups…
Factoriality and the Pin-Reutenauer procedure
J. Almeida, J. C. Costa, M. Zeitoun
We consider implicit signatures over finite semigroups determined by sets of pseudonatural numbers. We prove that, under relatively simple hypotheses on a pseudovariety V of semigr…
Hexagonal Projected Symmetries
Juliane F. Oliveira, Sofia S. B. S. D. Castro, Isabel S. Labouriau
In the study of pattern formation in symmetric physical systems a 3-dimensional structure in thin domains is often modelled as 2-dimensional one. We are concerned with functions in…