Reducibility of pointlike problems

• Main Author: Almeida, Jorge
• Publication Date: 2017
• Other Authors: Costa, José Carlos, Zeitoun, Marc
• Format: Article
• Language: eng
• Source: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Download full: http://hdl.handle.net/1822/38218
• topic: Pseudovariety; Profinite semigroup; Pointlike set; Regular language; Aperiodic semigroup; Ciências Naturais::Matemáticas; Ciências Naturais::Ciências da Computação e da Informação; Science & Technology

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 fi nite semigroups in which the order of every subgroup is a product of elements of a fi xed set of primes; the pseudovariety of all fi nite semigroups in which every regular J-class is the product of a rectangular band by a group from a fixed pseudovariety of groups that is reducible for the pointlike problem, respectively graph reducible. Allowing only trivial groups, we obtain omega-reducibility of the pointlike and idempotent pointlike problems, respectively for the pseudovarieties of all finite aperiodic semigroups (A) and of all finite semigroups in which all regular elements are idempotents (DA).