12 citations · 23 across the 10 of their papers we have counts for
10 papers
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…
The linear nature of pseudowords
Jorge Almeida, Alfredo Costa, José Carlos Costa +1
Given a pseudoword over suitable pseudovarieties, we associate to it a labeled linear order determined by the factorizations of the pseudoword. We show that, in the case of the pse…
On -reducibility of pseudovarieties of the form
José Carlos Costa, Conceição Nogueira, M. Lurdes Teixeira
This paper deals with the reducibility property of semidirect products of the form relatively to graph equation systems, where denotes the pseudovariety of de…
The word problem for -terms over the pseudovariety of local groups
J. C. Costa, C. Nogueira, M. L. Teixeira
In this paper we study the -word problem for the pseudovariety of local groups, where is the canonical signature consisting of the multiplication and the pseudoin…
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 …
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…
McCammond's normal forms for free aperiodic semigroups revisited
Jorge Almeida, José Carlos Costa, Marc Zeitoun
This paper revisits the solution of the word problem for -terms interpreted over finite aperiodic semigroups, obtained by J. McCammond. The original proof of correctness of McCa…
Semigroup presentations for test local groups
J. C. Costa, C. Nogueira, M. L. Teixeira
In this paper we exhibit a type of semigroup presentations which determines a class of local groups. We show that the finite elements of this class generate the pseudovariety ${\bf…
Canonical forms for free κ-semigroups
José Carlos Costa
The implicit signature k consists of the multiplication and the (ω-1)-power. We describe a procedure to transform each κ-term over a finite alphabet A into a certain canonical form…