Journal of Automated Reasoning

, Volume 62, Issue 4, pp 531–555 | Cite as

A Consistent Foundation for Isabelle/HOL

  • Ondřej Kunčar
  • Andrei PopescuEmail author


The interactive theorem prover Isabelle/HOL is based on the well understood higher-order logic (HOL), which is widely believed to be consistent (and provably consistent in set theory by a standard semantic argument). However, Isabelle/HOL brings its own personal touch to HOL: overloaded constant definitions, used to provide the users with Haskell-like type classes. These features are a delight for the users, but unfortunately are not easy to get right as an extension of HOL—they have a history of inconsistent behavior. It has been an open question under which criteria overloaded constant definitions and type definitions can be combined together while still guaranteeing consistency. This paper presents a solution to this problem: non-overlapping definitions and termination of the definition-dependency relation (tracked not only through constants but also through types) ensures relative consistency of Isabelle/HOL.


Higher-order logic Theorem proving Isabelle/HOL Consistency Model-theoretic semantics Ad hoc overloading 



We thank the reviewers for their useful comments and suggestions, and for catching some errors in the proofs. The anonymous ITP 2015 and Makarius Wenzel also made useful comments on the conference version of the paper. We thank Tobias Nipkow, Larry Paulson and Makarius Wenzel for inspiring discussions. This paper was partially supported by the DFG Grant Ni 491/13-3 and by the EPSRC grant EP/N019547/1.


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Authors and Affiliations

  1. 1.Fakultät für InformatikTechnische Universität MünchenMünchenGermany
  2. 2.Department of Computer Science, School of Science and TechnologyMiddlesex UniversityLondonUK
  3. 3.Institute of Mathematics Simion Stoilow of the Romanian AcademyBucharestRomania

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