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Author(s): Almeida, J
Klima, O
Title: Reducibility vs. definability for pseudovarieties of semigroups
Issue Date: 2016
Abstract: It is easy to show that a pseudovariety which is reducible with respect to an implicit signature sigma for the equation x = y can also be defined by sigma-identities. We present several negative examples for the converse using signatures in which the pseudovarieties are usually defined. An ordered example issue from the extended Straubing-Therien hierarchy of regular languages is also shown to provide a positive example for the inequality x <= y.
Document Type: Artigo em Revista Científica Internacional
Rights: openAccess
Appears in Collections:FCUP - Artigo em Revista Científica Internacional

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