Formal Languages, Formally and Coinductively

Author Dmitriy Traytel

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Dmitriy Traytel

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Dmitriy Traytel. Formal Languages, Formally and Coinductively. In 1st International Conference on Formal Structures for Computation and Deduction (FSCD 2016). Leibniz International Proceedings in Informatics (LIPIcs), Volume 52, pp. 31:1-31:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2016)


Traditionally, formal languages are defined as sets of words. More recently, the alternative coalgebraic or coinductive representation as infinite tries, i.e., prefix trees branching over the alphabet, has been used to obtain compact and elegant proofs of classic results in language theory. In this paper, we study this representation in the Isabelle proof assistant. We define regular operations on infinite tries and prove the axioms of Kleene algebra for those operations. Thereby, we exercise corecursion and coinduction and confirm the coinductive view being profitable in formalizations, as it improves over the set-of-words view with respect to proof automation.
  • Formal languages
  • codatatypes
  • corecursion
  • coinduction
  • interactive theorem proving
  • Isabelle HOL


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