Varieties and Covarieties of Languages (Extended Abstract)

  • Authors:
  • Jan Rutten;Adolfo Ballester-Bolinches;Enric Cosme-Llópez

  • Affiliations:
  • -;-;-

  • Venue:
  • Electronic Notes in Theoretical Computer Science (ENTCS)
  • Year:
  • 2013

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Abstract

Because of the isomorphism (XxA)-X@?X-(A-X), the transition structure of a deterministic automaton with state set X and with inputs from an alphabet A can be viewed both as an algebra and as a coalgebra. This algebra-coalgebra duality goes back to Arbib and Manes, who formulated it as a duality between reachability and observability, and is ultimately based on Kalman@?s duality in systems theory between controllability and observability. Recently, it was used to give a new proof of Brzozowski@?s minimization algorithm for deterministic automata. Here we will use the algebra-coalgebra duality of automata as a common perspective for the study of both varieties and covarieties, which are classes of automata and languages defined by equations and coequations, respectively. We make a first connection with Eilenberg@?s definition of varieties of languages, which is based on the classical, algebraic notion of varieties of (transition) monoids.