On Corecursive Algebras for Functors Preserving Coproducts

Authors Jiri Adámek, Stefan Milius

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Jiri Adámek
Stefan Milius

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Jiri Adámek and Stefan Milius. On Corecursive Algebras for Functors Preserving Coproducts. In 7th Conference on Algebra and Coalgebra in Computer Science (CALCO 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 72, pp. 3:1-3:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2017)


For an endofunctor H on a hyper-extensive category preserving countable coproducts we describe the free corecursive algebra on Y as the coproduct of the terminal coalgebra for H and the free H-algebra on Y. As a consequence, we derive that H is a cia functor, i.e., its corecursive algebras are precisely the cias (completely iterative algebras). Also all functors H(-) + Y are then cia functors. For finitary set functors we prove that, conversely, if H is a cia functor, then it has the form H = W \times (-) + Y for some sets W and Y.
  • terminal coalgebra
  • free algebra
  • corecursive algebra
  • hyper-extensive category


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