Fibrational Initial Algebra-Final Coalgebra Coincidence over Initial Algebras: Turning Verification Witnesses Upside Down

Authors Mayuko Kori , Ichiro Hasuo , Shin-ya Katsumata

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Mayuko Kori
  • The Graduate University for Advanced Studies (SOKENDAI), Hayama, Japan
  • National Institute of Informatics, Tokyo, Japan
Ichiro Hasuo
  • The Graduate University for Advanced Studies (SOKENDAI), Hayama, Japan
  • National Institute of Informatics, Tokyo, Japan
Shin-ya Katsumata
  • National Institute of Informatics, Tokyo, Japan

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Mayuko Kori, Ichiro Hasuo, and Shin-ya Katsumata. Fibrational Initial Algebra-Final Coalgebra Coincidence over Initial Algebras: Turning Verification Witnesses Upside Down. In 32nd International Conference on Concurrency Theory (CONCUR 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 203, pp. 21:1-21:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)


The coincidence between initial algebras (IAs) and final coalgebras (FCs) is a phenomenon that underpins various important results in theoretical computer science. In this paper, we identify a general fibrational condition for the IA-FC coincidence, namely in the fiber over an initial algebra in the base category. Identifying (co)algebras in a fiber as (co)inductive predicates, our fibrational IA-FC coincidence allows one to use coinductive witnesses (such as invariants) for verifying inductive properties (such as liveness). Our general fibrational theory features the technical condition of stability of chain colimits; we extend the framework to the presence of a monadic effect, too, restricting to fibrations of complete lattice-valued predicates. Practical benefits of our categorical theory are exemplified by new "upside-down" witness notions for three verification problems: probabilistic liveness, and acceptance and model-checking with respect to bottom-up tree automata.

Subject Classification

ACM Subject Classification
  • Theory of computation → Categorical semantics
  • initial algebra
  • final coalgebra
  • fibration
  • category theory


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