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|Title:||Reducibility vs. definability for pseudovarieties of semigroups|
|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|
|Appears in Collections:||FCUP - Artigo em Revista Científica Internacional|
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